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< title > Iterator Facade and Adaptor< / title >
< meta name = "author" content = "David Abrahams, Jeremy Siek, Thomas Witt" / >
< meta name = "organization" content = "Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" / >
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< h1 class = "title" > Iterator Facade and Adaptor< / h1 >
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< tr > < th class = "docinfo-name" > Author:< / th >
< td > David Abrahams, Jeremy Siek, Thomas Witt< / td > < / tr >
< tr > < th class = "docinfo-name" > Contact:< / th >
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< td > < a class = "first reference" href = "mailto:dave@boost-consulting.com" > dave@ boost-consulting.com< / a > , < a class = "reference" href = "mailto:jsiek@osl.iu.edu" > jsiek@ osl.iu.edu< / a > , < a class = "last reference" href = "mailto:witt@acm.org" > witt@ acm.org< / a > < / td > < / tr >
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< tr > < th class = "docinfo-name" > Organization:< / th >
< td > < a class = "first reference" href = "http://www.boost-consulting.com" > Boost Consulting< / a > , Indiana University < a class = "reference" href = "http://www.osl.iu.edu" > Open Systems
Lab< / a > , University of Hanover < a class = "last reference" href = "http://www.ive.uni-hannover.de" > Institute for Transport
Railway Operation and Construction< / a > < / td > < / tr >
< tr > < th class = "docinfo-name" > Date:< / th >
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< td > 2004-01-13< / td > < / tr >
2003-11-24 06:02:46 +01:00
< tr class = "field" > < th class = "docinfo-name" > Number:< / th > < td class = "field-body" > This is a revised version of < a class = "reference" href = "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/papers/2003/n1530.html" > N1530< / a > =03-0113, which was
accepted for Technical Report 1 by the C++ standard
committee's library working group.< / td >
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< / tbody >
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n1530_, the paper accepted by the LWG. -->
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< tr class = "field" > < th class = "field-name" > copyright:< / th > < td class = "field-body" > Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All rights reserved< / td >
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< tr class = "field" > < th class = "field-name" > abstract:< / th > < td class = "field-body" > We propose a set of class templates that help programmers
build standard-conforming iterators, both from scratch and
by adapting other iterators.< / td >
< / tr >
< / tbody >
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< div class = "contents topic" id = "table-of-contents" >
< p class = "topic-title" > < a name = "table-of-contents" > Table of Contents< / a > < / p >
< ul class = "simple" >
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< li > < a class = "reference" href = "#motivation" id = "id14" name = "id14" > Motivation< / a > < / li >
< li > < a class = "reference" href = "#impact-on-the-standard" id = "id15" name = "id15" > Impact on the Standard< / a > < / li >
< li > < a class = "reference" href = "#design" id = "id16" name = "id16" > Design< / a > < ul >
< li > < a class = "reference" href = "#iterator-concepts" id = "id17" name = "id17" > Iterator Concepts< / a > < / li >
< li > < a class = "reference" href = "#interoperability" id = "id18" name = "id18" > Interoperability< / a > < / li >
< li > < a class = "reference" href = "#iterator-facade" id = "id19" name = "id19" > Iterator Facade< / a > < ul >
< li > < a class = "reference" href = "#usage" id = "id20" name = "id20" > Usage< / a > < / li >
< li > < a class = "reference" href = "#iterator-core-access" id = "id21" name = "id21" > Iterator Core Access< / a > < / li >
< li > < a class = "reference" href = "#operator" id = "id22" name = "id22" > < tt class = "literal" > < span class = "pre" > operator[]< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#id6" id = "id23" name = "id23" > < tt class = "literal" > < span class = "pre" > operator-> < / span > < / tt > < / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#iterator-adaptor" id = "id24" name = "id24" > Iterator Adaptor< / a > < / li >
< li > < a class = "reference" href = "#specialized-adaptors" id = "id25" name = "id25" > Specialized Adaptors< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#proposed-text" id = "id26" name = "id26" > Proposed Text< / a > < ul >
< li > < a class = "reference" href = "#header-iterator-helper-synopsis-lib-iterator-helper-synopsis" id = "id27" name = "id27" > Header < tt class = "literal" > < span class = "pre" > < iterator_helper> < / span > < / tt > synopsis [lib.iterator.helper.synopsis]< / a > < / li >
< li > < a class = "reference" href = "#iterator-facade-lib-iterator-facade" id = "id28" name = "id28" > Iterator facade [lib.iterator.facade]< / a > < ul >
< li > < a class = "reference" href = "#class-template-iterator-facade" id = "id29" name = "id29" > Class template < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#iterator-facade-requirements" id = "id30" name = "id30" > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > Requirements< / a > < / li >
< li > < a class = "reference" href = "#iterator-facade-operations" id = "id31" name = "id31" > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#iterator-adaptor-lib-iterator-adaptor" id = "id32" name = "id32" > Iterator adaptor [lib.iterator.adaptor]< / a > < ul >
< li > < a class = "reference" href = "#class-template-iterator-adaptor" id = "id33" name = "id33" > Class template < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#iterator-adaptor-requirements" id = "id34" name = "id34" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#iterator-adaptor-base-class-parameters" id = "id35" name = "id35" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > base class parameters< / a > < / li >
< li > < a class = "reference" href = "#iterator-adaptor-models" id = "id36" name = "id36" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#iterator-adaptor-public-operations" id = "id37" name = "id37" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > public operations< / a > < / li >
< li > < a class = "reference" href = "#iterator-adaptor-protected-member-functions" id = "id38" name = "id38" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > protected member functions< / a > < / li >
< li > < a class = "reference" href = "#iterator-adaptor-private-member-functions" id = "id39" name = "id39" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > private member functions< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#specialized-adaptors-lib-iterator-special-adaptors" id = "id40" name = "id40" > Specialized adaptors [lib.iterator.special.adaptors]< / a > < ul >
< li > < a class = "reference" href = "#indirect-iterator" id = "id41" name = "id41" > Indirect iterator< / a > < ul >
< li > < a class = "reference" href = "#class-template-pointee" id = "id42" name = "id42" > Class template < tt class = "literal" > < span class = "pre" > pointee< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#class-template-indirect-reference" id = "id43" name = "id43" > Class template < tt class = "literal" > < span class = "pre" > indirect_reference< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#class-template-indirect-iterator" id = "id44" name = "id44" > Class template < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#indirect-iterator-requirements" id = "id45" name = "id45" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#indirect-iterator-models" id = "id46" name = "id46" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#indirect-iterator-operations" id = "id47" name = "id47" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#reverse-iterator" id = "id48" name = "id48" > Reverse iterator< / a > < ul >
< li > < a class = "reference" href = "#class-template-reverse-iterator" id = "id49" name = "id49" > Class template < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#reverse-iterator-requirements" id = "id50" name = "id50" > < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#reverse-iterator-models" id = "id51" name = "id51" > < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#reverse-iterator-operations" id = "id52" name = "id52" > < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#transform-iterator" id = "id53" name = "id53" > Transform iterator< / a > < ul >
< li > < a class = "reference" href = "#class-template-transform-iterator" id = "id54" name = "id54" > Class template < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#transform-iterator-requirements" id = "id55" name = "id55" > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#transform-iterator-models" id = "id56" name = "id56" > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#transform-iterator-operations" id = "id57" name = "id57" > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#filter-iterator" id = "id58" name = "id58" > Filter iterator< / a > < ul >
< li > < a class = "reference" href = "#class-template-filter-iterator" id = "id59" name = "id59" > Class template < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#filter-iterator-requirements" id = "id60" name = "id60" > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#filter-iterator-models" id = "id61" name = "id61" > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#filter-iterator-operations" id = "id62" name = "id62" > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#counting-iterator" id = "id63" name = "id63" > Counting iterator< / a > < ul >
< li > < a class = "reference" href = "#class-template-counting-iterator" id = "id64" name = "id64" > Class template < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#counting-iterator-requirements" id = "id65" name = "id65" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#counting-iterator-models" id = "id66" name = "id66" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#counting-iterator-operations" id = "id67" name = "id67" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
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< li > < a class = "reference" href = "#function-output-iterator" id = "id68" name = "id68" > Function output iterator< / a > < ul >
< li > < a class = "reference" href = "#class-template-function-output-iterator" id = "id69" name = "id69" > Class template < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > < / a > < / li >
< li > < a class = "reference" href = "#function-output-iterator-requirements" id = "id70" name = "id70" > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > requirements< / a > < / li >
< li > < a class = "reference" href = "#function-output-iterator-models" id = "id71" name = "id71" > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > models< / a > < / li >
< li > < a class = "reference" href = "#function-output-iterator-operations" id = "id72" name = "id72" > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > operations< / a > < / li >
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< / ul >
< / li >
< / ul >
< / li >
< / ul >
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< / li >
< / ul >
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< / div >
< div class = "section" id = "motivation" >
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< h1 > < a class = "toc-backref" href = "#id14" name = "motivation" > Motivation< / a > < / h1 >
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< p > Iterators play an important role in modern C++ programming. The
iterator is the central abstraction of the algorithms of the Standard
Library, allowing algorithms to be re-used in in a wide variety of
contexts. The C++ Standard Library contains a wide variety of useful
iterators. Every one of the standard containers comes with constant
and mutable iterators < a class = "footnote-reference" href = "#mutable" id = "id1" name = "id1" > < sup > 2< / sup > < / a > , and also reverse versions of those
same iterators which traverse the container in the opposite direction.
The Standard also supplies < tt class = "literal" > < span class = "pre" > istream_iterator< / span > < / tt > and
< tt class = "literal" > < span class = "pre" > ostream_iterator< / span > < / tt > for reading from and writing to streams,
< tt class = "literal" > < span class = "pre" > insert_iterator< / span > < / tt > , < tt class = "literal" > < span class = "pre" > front_insert_iterator< / span > < / tt > and
< tt class = "literal" > < span class = "pre" > back_insert_iterator< / span > < / tt > for inserting elements into containers, and
< tt class = "literal" > < span class = "pre" > raw_storage_iterator< / span > < / tt > for initializing raw memory [7].< / p >
< p > Despite the many iterators supplied by the Standard Library, obvious
and useful iterators are missing, and creating new iterator types is
still a common task for C++ programmers. The literature documents
several of these, for example line_iterator [3] and Constant_iterator
[9]. The iterator abstraction is so powerful that we expect
programmers will always need to invent new iterator types.< / p >
< p > Although it is easy to create iterators that < em > almost< / em > conform to the
standard, the iterator requirements contain subtleties which can make
creating an iterator which < em > actually< / em > conforms quite difficult.
Further, the iterator interface is rich, containing many operators
that are technically redundant and tedious to implement. To automate
the repetitive work of constructing iterators, we propose
< tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > , an iterator base class template which provides
the rich interface of standard iterators and delegates its
implementation to member functions of the derived class. In addition
to reducing the amount of code necessary to create an iterator, the
< tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > also provides compile-time error detection.
Iterator implementation mistakes that often go unnoticed are turned
into compile-time errors because the derived class implementation must
match the expectations of the < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > .< / p >
< p > A common pattern of iterator construction is the adaptation of one
iterator to form a new one. The functionality of an iterator is
composed of four orthogonal aspects: traversal, indirection, equality
comparison and distance measurement. Adapting an old iterator to
create a new one often saves work because one can reuse one aspect of
functionality while redefining the other. For example, the Standard
provides < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > , which adapts any Bidirectional Iterator
by inverting its direction of traversal. As with plain iterators,
iterator adaptors defined outside the Standard have become commonplace
in the literature:< / p >
< ul class = "simple" >
< li > Checked iter[13] adds bounds-checking to an existing iterator.< / li >
< li > The iterators of the View Template Library[14], which adapts
containers, are themselves adaptors over the underlying iterators.< / li >
< li > Smart iterators [5] adapt an iterator's dereferencing behavior by
applying a function object to the object being referenced and
returning the result.< / li >
< li > Custom iterators [4], in which a variety of adaptor types are enumerated.< / li >
< li > Compound iterators [1], which access a slice out of a container of containers.< / li >
< li > Several iterator adaptors from the MTL [12]. The MTL contains a
strided iterator, where each call to < tt class = "literal" > < span class = "pre" > operator++()< / span > < / tt > moves the
iterator ahead by some constant factor, and a scaled iterator, which
multiplies the dereferenced value by some constant.< / li >
< / ul >
< table class = "footnote" frame = "void" id = "concept" rules = "none" >
< colgroup > < col class = "label" / > < col / > < / colgroup >
< tbody valign = "top" >
< tr > < td class = "label" > < a name = "concept" > [1]< / a > < / td > < td > We use the term concept to mean a set of requirements
that a type must satisfy to be used with a particular template
parameter.< / td > < / tr >
< / tbody >
< / table >
< table class = "footnote" frame = "void" id = "mutable" rules = "none" >
< colgroup > < col class = "label" / > < col / > < / colgroup >
< tbody valign = "top" >
< tr > < td class = "label" > < a class = "fn-backref" href = "#id1" name = "mutable" > [2]< / a > < / td > < td > The term mutable iterator refers to iterators over objects that
can be changed by assigning to the dereferenced iterator, while
constant iterator refers to iterators over objects that cannot be
modified.< / td > < / tr >
< / tbody >
< / table >
< p > To fulfill the need for constructing adaptors, we propose the
< tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > class template. Instantiations of
< tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > serve as a base classes for new iterators,
providing the default behavior of forwarding all operations to the
underlying iterator. The user can selectively replace these features
in the derived iterator class. This proposal also includes a number
of more specialized adaptors, such as the < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > that
applies some user-specified function during the dereference of the
iterator.< / p >
< / div >
< div class = "section" id = "impact-on-the-standard" >
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< h1 > < a class = "toc-backref" href = "#id15" name = "impact-on-the-standard" > Impact on the Standard< / a > < / h1 >
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< p > This proposal is purely an addition to the C++ standard library.
However, note that this proposal relies on the proposal for New
Iterator Concepts.< / p >
< / div >
< div class = "section" id = "design" >
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< h1 > < a class = "toc-backref" href = "#id16" name = "design" > Design< / a > < / h1 >
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< div class = "section" id = "iterator-concepts" >
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< h2 > < a class = "toc-backref" href = "#id17" name = "iterator-concepts" > Iterator Concepts< / a > < / h2 >
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< p > This proposal is formulated in terms of the new < tt class = "literal" > < span class = "pre" > iterator< / span > < span class = "pre" > concepts< / span > < / tt >
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as proposed in < a class = "reference" href = "http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html" > n1550< / a > , since user-defined and especially adapted
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iterators suffer from the well known categorization problems that are
inherent to the current iterator categories.< / p >
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< p > This proposal does not strictly depend on proposal < a class = "reference" href = "http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html" > n1550< / a > , as there
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is a direct mapping between new and old categories. This proposal
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could be reformulated using this mapping if < a class = "reference" href = "http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html" > n1550< / a > was not accepted.< / p >
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< / div >
< div class = "section" id = "interoperability" >
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< h2 > < a class = "toc-backref" href = "#id18" name = "interoperability" > Interoperability< / a > < / h2 >
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< p > The question of iterator interoperability is poorly addressed in the
current standard. There are currently two defect reports that are
concerned with interoperability issues.< / p >
< p > Issue < a class = "reference" href = "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#179" > 179< / a > concerns the fact that mutable container iterator types
are only required to be convertible to the corresponding constant
iterator types, but objects of these types are not required to
interoperate in comparison or subtraction expressions. This situation
is tedious in practice and out of line with the way built in types
work. This proposal implements the proposed resolution to issue
< a class = "reference" href = "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-defects.html#179" > 179< / a > , as most standard library implementations do nowadays. In other
words, if an iterator type A has an implicit or user defined
conversion to an iterator type B, the iterator types are interoperable
and the usual set of operators are available.< / p >
< p > Issue < a class = "reference" href = "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#280" > 280< / a > concerns the current lack of interoperability between
reverse iterator types. The proposed new reverse_iterator template
fixes the issues raised in 280. It provides the desired
interoperability without introducing unwanted overloads.< / p >
< / div >
< div class = "section" id = "iterator-facade" >
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< h2 > < a class = "toc-backref" href = "#id19" name = "iterator-facade" > Iterator Facade< / a > < / h2 >
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<!-- Version 1.1 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG for TR1. -->
<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
rights reserved -->
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< p > While the iterator interface is rich, there is a core subset of the
interface that is necessary for all the functionality. We have
identified the following core behaviors for iterators:< / p >
< ul class = "simple" >
< li > dereferencing< / li >
< li > incrementing< / li >
< li > decrementing< / li >
< li > equality comparison< / li >
< li > random-access motion< / li >
< li > distance measurement< / li >
< / ul >
< p > In addition to the behaviors listed above, the core interface elements
include the associated types exposed through iterator traits:
< tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > , < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > , < tt class = "literal" > < span class = "pre" > difference_type< / span > < / tt > , and
< tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > .< / p >
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< p > Iterator facade uses the Curiously Recurring Template
Pattern (CRTP) < a class = "citation-reference" href = "#cop95" id = "id4" name = "id4" > [Cop95]< / a > so that the user can specify the behavior
of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > in a derived class. Former designs used
policy objects to specify the behavior, but that approach was
discarded for several reasons:< / p >
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< blockquote >
< ol class = "arabic simple" >
< li > the creation and eventual copying of the policy object may create
overhead that can be avoided with the current approach.< / li >
< li > The policy object approach does not allow for custom constructors
on the created iterator types, an essential feature if
< tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > should be used in other library
implementations.< / li >
< li > Without the use of CRTP, the standard requirement that an
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iterator's < tt class = "literal" > < span class = "pre" > operator++< / span > < / tt > returns the iterator type itself
would mean that all iterators built with the library would
have to be specializations of < tt class = "literal" > < span class = "pre" > iterator_facade< ...> < / span > < / tt > , rather
than something more descriptive like
< tt class = "literal" > < span class = "pre" > indirect_iterator< T*> < / span > < / tt > . Cumbersome type generator
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metafunctions would be needed to build new parameterized
iterators, and a separate < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > layer would be
impossible.< / li >
< / ol >
< / blockquote >
< div class = "section" id = "usage" >
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< h3 > < a class = "toc-backref" href = "#id20" name = "usage" > Usage< / a > < / h3 >
2004-01-10 20:00:48 +01:00
< p > The user of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > derives his iterator class from a
specialization of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > and passes the derived
iterator class as < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > 's first template parameter.
The order of the other template parameters have been carefully
chosen to take advantage of useful defaults. For example, when
defining a constant lvalue iterator, the user can pass a
const-qualified version of the iterator's < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > as
< tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > 's < tt class = "literal" > < span class = "pre" > Value< / span > < / tt > parameter and omit the
< tt class = "literal" > < span class = "pre" > Reference< / span > < / tt > parameter which follows.< / p >
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< p > The derived iterator class must define member functions implementing
the iterator's core behaviors. The following table describes
expressions which are required to be valid depending on the category
of the derived iterator type. These member functions are described
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briefly below and in more detail in the iterator facade
requirements.< / p >
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< blockquote >
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< table border class = "table" >
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< colgroup >
< col width = "44%" / >
< col width = "56%" / >
< / colgroup >
< thead valign = "bottom" >
< tr > < th > Expression< / th >
< th > Effects< / th >
< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > < tt class = "literal" > < span class = "pre" > i.dereference()< / span > < / tt > < / td >
< td > Access the value referred to< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > i.equal(j)< / span > < / tt > < / td >
< td > Compare for equality with < tt class = "literal" > < span class = "pre" > j< / span > < / tt > < / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > i.increment()< / span > < / tt > < / td >
< td > Advance by one position< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > i.decrement()< / span > < / tt > < / td >
< td > Retreat by one position< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > i.advance(n)< / span > < / tt > < / td >
< td > Advance by < tt class = "literal" > < span class = "pre" > n< / span > < / tt > positions< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > i.distance_to(j)< / span > < / tt > < / td >
< td > Measure the distance to < tt class = "literal" > < span class = "pre" > j< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< / blockquote >
<!-- Should we add a comment that a zero overhead implementation of iterator_facade
is possible with proper inlining? -->
< p > In addition to implementing the core interface functions, an iterator
derived from < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > typically defines several
constructors. To model any of the standard iterator concepts, the
iterator must at least have a copy constructor. Also, if the iterator
type < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is meant to be automatically interoperate with another
iterator type < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > (as with constant and mutable iterators) then
there must be an implicit conversion from < tt class = "literal" > < span class = "pre" > X< / span > < / tt > to < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > or from < tt class = "literal" > < span class = "pre" > Y< / span > < / tt >
to < tt class = "literal" > < span class = "pre" > X< / span > < / tt > (but not both), typically implemented as a conversion
constructor. Finally, if the iterator is to model Forward Traversal
Iterator or a more-refined iterator concept, a default constructor is
required.< / p >
< / div >
< div class = "section" id = "iterator-core-access" >
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< h3 > < a class = "toc-backref" href = "#id21" name = "iterator-core-access" > Iterator Core Access< / a > < / h3 >
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< p > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > and the operator implementations need to be able
to access the core member functions in the derived class. Making the
core member functions public would expose an implementation detail to
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the user. The design used here ensures that implementation details do
not appear in the public interface of the derived iterator type.< / p >
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< p > Preventing direct access to the core member functions has two
advantages. First, there is no possibility for the user to accidently
use a member function of the iterator when a member of the value_type
was intended. This has been an issue with smart pointer
implementations in the past. The second and main advantage is that
library implementers can freely exchange a hand-rolled iterator
implementation for one based on < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > without fear of
breaking code that was accessing the public core member functions
directly.< / p >
< p > In a naive implementation, keeping the derived class' core member
functions private would require it to grant friendship to
< tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > and each of the seven operators. In order to
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reduce the burden of limiting access, < tt class = "literal" > < span class = "pre" > iterator_core_access< / span > < / tt > is
provided, a class that acts as a gateway to the core member functions
in the derived iterator class. The author of the derived class only
needs to grant friendship to < tt class = "literal" > < span class = "pre" > iterator_core_access< / span > < / tt > to make his core
member functions available to the library.< / p >
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<!-- This is no long uptodate - thw -->
<!-- Yes it is; I made sure of it! - DWA -->
< p > < tt class = "literal" > < span class = "pre" > iterator_core_access< / span > < / tt > will be typically implemented as an empty
class containing only private static member functions which invoke the
iterator core member functions. There is, however, no need to
standardize the gateway protocol. Note that even if
< tt class = "literal" > < span class = "pre" > iterator_core_access< / span > < / tt > used public member functions it would not
open a safety loophole, as every core member function preserves the
invariants of the iterator.< / p >
< / div >
< div class = "section" id = "operator" >
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< h3 > < a class = "toc-backref" href = "#id22" name = "operator" > < tt class = "literal" > < span class = "pre" > operator[]< / span > < / tt > < / a > < / h3 >
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< p > The indexing operator for a generalized iterator presents special
challenges. A random access iterator's < tt class = "literal" > < span class = "pre" > operator[]< / span > < / tt > is only
required to return something convertible to its < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > .
Requiring that it return an lvalue would rule out currently-legal
random-access iterators which hold the referenced value in a data
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member (e.g. < a class = "reference" href = "#counting" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > < / a > ), because < tt class = "literal" > < span class = "pre" > *(p+n)< / span > < / tt > is a reference
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into the temporary iterator < tt class = "literal" > < span class = "pre" > p+n< / span > < / tt > , which is destroyed when
< tt class = "literal" > < span class = "pre" > operator[]< / span > < / tt > returns.< / p >
< p > Writable iterators built with < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > implement the
semantics required by the preferred resolution to < a class = "reference" href = "http://anubis.dkuug.dk/jtc1/sc22/wg21/docs/lwg-active.html#299" > issue 299< / a > and
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adopted by proposal < a class = "reference" href = "http://anubis.dkuug.dk/JTC1/SC22/WG21/docs/papers/2003/n1550.html" > n1550< / a > : the result of < tt class = "literal" > < span class = "pre" > p[n]< / span > < / tt > is an object
convertible to the iterator's < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > p[n]< / span > < span class = "pre" > =< / span > < span class = "pre" > x< / span > < / tt > is
equivalent to < tt class = "literal" > < span class = "pre" > *(p< / span > < span class = "pre" > +< / span > < span class = "pre" > n)< / span > < span class = "pre" > =< / span > < span class = "pre" > x< / span > < / tt > (Note: This result object may be
implemented as a proxy containing a copy of < tt class = "literal" > < span class = "pre" > p+n< / span > < / tt > ). This approach
will work properly for any random-access iterator regardless of the
other details of its implementation. A user who knows more about
the implementation of her iterator is free to implement an
< tt class = "literal" > < span class = "pre" > operator[]< / span > < / tt > that returns an lvalue in the derived iterator
class; it will hide the one supplied by < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > from
clients of her iterator.< / p >
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< a class = "target" id = "operator-arrow" name = "operator-arrow" > < / a > < / div >
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< div class = "section" id = "id6" >
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< h3 > < a class = "toc-backref" href = "#id23" name = "id6" > < tt class = "literal" > < span class = "pre" > operator-> < / span > < / tt > < / a > < / h3 >
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< p > The < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > type of a readable iterator (and today's input
iterator) need not in fact be a reference, so long as it is
convertible to the iterator's < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > . When the < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt >
is a class, however, it must still be possible to access members
through < tt class = "literal" > < span class = "pre" > operator-> < / span > < / tt > . Therefore, an iterator whose < tt class = "literal" > < span class = "pre" > reference< / span > < / tt >
type is not in fact a reference must return a proxy containing a copy
of the referenced value from its < tt class = "literal" > < span class = "pre" > operator-> < / span > < / tt > .< / p >
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< p > The return types for < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > 's < tt class = "literal" > < span class = "pre" > operator-> < / span > < / tt > and
< tt class = "literal" > < span class = "pre" > operator[]< / span > < / tt > are not explicitly specified. Instead, those types
are described in terms of a set of requirements, which must be
satisfied by the < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > implementation.< / p >
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< table class = "citation" frame = "void" id = "cop95" rules = "none" >
< colgroup > < col class = "label" / > < col / > < / colgroup >
< col / >
< tbody valign = "top" >
< tr > < td class = "label" > < a class = "fn-backref" href = "#id4" name = "cop95" > [Cop95]< / a > < / td > < td > [Coplien, 1995] Coplien, J., Curiously Recurring Template
Patterns, C++ Report, February 1995, pp. 24-27.< / td > < / tr >
< / tbody >
< / table >
< / div >
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< / div >
< div class = "section" id = "iterator-adaptor" >
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< h2 > < a class = "toc-backref" href = "#id24" name = "iterator-adaptor" > Iterator Adaptor< / a > < / h2 >
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<!-- Version 1.2 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG for TR1. -->
<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
rights reserved -->
< p > The < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > class template adapts some < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > < a class = "footnote-reference" href = "#base" id = "id7" name = "id7" > < sup > 3< / sup > < / a >
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type to create a new iterator. Instantiations of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt >
are derived from a corresponding instantiation of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt >
and implement the core behaviors in terms of the < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > type. In
essence, < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > merely forwards all operations to an
instance of the < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > type, which it stores as a member.< / p >
< table class = "footnote" frame = "void" id = "base" rules = "none" >
< colgroup > < col class = "label" / > < col / > < / colgroup >
< tbody valign = "top" >
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< tr > < td class = "label" > < a class = "fn-backref" href = "#id7" name = "base" > [3]< / a > < / td > < td > The term " Base" here does not refer to a base class and is
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not meant to imply the use of derivation. We have followed the lead
of the standard library, which provides a base() function to access
the underlying iterator object of a < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > adaptor.< / td > < / tr >
< / tbody >
< / table >
< p > The user of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > creates a class derived from an
instantiation of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > and then selectively
redefines some of the core member functions described in the table
above. The < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > type need not meet the full requirements for an
iterator. It need only support the operations used by the core
interface functions of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > that have not been
redefined in the user's derived class.< / p >
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< p > Several of the template parameters of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > default
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to < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > . This allows the
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user to make use of a default parameter even when she wants to
specify a parameter later in the parameter list. Also, the
defaults for the corresponding associated types are somewhat
complicated, so metaprogramming is required to compute them, and
< tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > can help to simplify the implementation. Finally,
the identity of the < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > type is not left unspecified
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because specification helps to highlight that the < tt class = "literal" > < span class = "pre" > Reference< / span > < / tt >
template parameter may not always be identical to the iterator's
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< tt class = "literal" > < span class = "pre" > reference< / span > < / tt > type, and will keep users from making mistakes based on
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that assumption.< / p >
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< / div >
< div class = "section" id = "specialized-adaptors" >
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< h2 > < a class = "toc-backref" href = "#id25" name = "specialized-adaptors" > Specialized Adaptors< / a > < / h2 >
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< p > This proposal also contains several examples of specialized adaptors
which were easily implemented using < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > :< / p >
< ul class = "simple" >
< li > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > , which iterates over iterators, pointers,
or smart pointers and applies an extra level of dereferencing.< / li >
< li > A new < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > , which inverts the direction of a Base
iterator's motion, while allowing adapted constant and mutable
iterators to interact in the expected ways (unlike those in most
implementations of C++98).< / li >
< li > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > , which applies a user-defined function object
to the underlying values when dereferenced.< / li >
< li > < tt class = "literal" > < span class = "pre" > projection_iterator< / span > < / tt > , which is similar to < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt >
except that when dereferenced it returns a reference instead of
a value.< / li >
< li > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > , which provides a view of an iterator range in
which some elements of the underlying range are skipped.< / li >
< / ul >
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< a class = "target" id = "counting" name = "counting" > < / a > < ul class = "simple" >
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< li > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > , which adapts any incrementable type
(e.g. integers, iterators) so that incrementing/decrementing the
adapted iterator and dereferencing it produces successive values of
the Base type.< / li >
< li > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > , which makes it easier to create custom
output iterators.< / li >
< / ul >
< p > Based on examples in the Boost library, users have generated many new
adaptors, among them a permutation adaptor which applies some
permutation to a random access iterator, and a strided adaptor, which
adapts a random access iterator by multiplying its unit of motion by a
constant factor. In addition, the Boost Graph Library (BGL) uses
iterator adaptors to adapt other graph libraries, such as LEDA [10]
and Stanford GraphBase [8], to the BGL interface (which requires C++
Standard compliant iterators).< / p >
< / div >
< / div >
< div class = "section" id = "proposed-text" >
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< h1 > < a class = "toc-backref" href = "#id26" name = "proposed-text" > Proposed Text< / a > < / h1 >
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< div class = "section" id = "header-iterator-helper-synopsis-lib-iterator-helper-synopsis" >
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< h2 > < a class = "toc-backref" href = "#id27" name = "header-iterator-helper-synopsis-lib-iterator-helper-synopsis" > Header < tt class = "literal" > < span class = "pre" > < iterator_helper> < / span > < / tt > synopsis [lib.iterator.helper.synopsis]< / a > < / h2 >
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< pre class = "literal-block" >
struct use_default;
struct iterator_core_access { /* implementation detail */ };
template <
class Derived
, class Value
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, class CategoryOrTraversal
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, class Reference = Value&
, class Difference = ptrdiff_t
>
class iterator_facade;
template <
class Derived
, class Base
, class Value = use_default
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, class CategoryOrTraversal = use_default
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, class Reference = use_default
, class Difference = use_default
>
class iterator_adaptor;
template <
class Iterator
, class Value = use_default
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, class CategoryOrTraversal = use_default
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, class Reference = use_default
, class Difference = use_default
>
class indirect_iterator;
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template < class Dereferenceable>
struct pointee;
template < class Dereferenceable>
struct indirect_reference;
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template < class Iterator>
class reverse_iterator;
template <
class UnaryFunction
, class Iterator
, class Reference = use_default
, class Value = use_default
>
class transform_iterator;
template < class Predicate, class Iterator>
class filter_iterator;
template <
class Incrementable
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, class CategoryOrTraversal = use_default
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, class Difference = use_default
>
class counting_iterator
template < class UnaryFunction>
class function_output_iterator;
< / pre >
< / div >
< div class = "section" id = "iterator-facade-lib-iterator-facade" >
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< h2 > < a class = "toc-backref" href = "#id28" name = "iterator-facade-lib-iterator-facade" > Iterator facade [lib.iterator.facade]< / a > < / h2 >
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< p > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > is a base class template that implements the
interface of standard iterators in terms of a few core functions
and associated types, to be supplied by a derived iterator class.< / p >
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< div class = "section" id = "class-template-iterator-facade" >
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< h3 > < a class = "toc-backref" href = "#id29" name = "class-template-iterator-facade" > Class template < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > < / a > < / h3 >
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<!-- Version 1.3 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG for TR1. -->
<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
rights reserved -->
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< pre class = "literal-block" >
template <
class Derived
, class Value
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, class CategoryOrTraversal
, class Reference = Value&
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, class Difference = ptrdiff_t
>
class iterator_facade {
public:
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typedef remove_const< Value> ::type value_type;
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typedef Reference reference;
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typedef Value* pointer;
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typedef Difference difference_type;
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typedef /* see < a class = "reference" href = "#iterator-category" > below< / a > */ iterator_category;
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reference operator*() const;
/* see < a class = "reference" href = "#operator-arrow" > below< / a > */ operator-> () const;
/* see < a class = "reference" href = "#brackets" > below< / a > */ operator[](difference_type n) const;
Derived& operator++();
Derived operator++(int);
Derived& operator--();
Derived operator--(int);
Derived& operator+=(difference_type n);
Derived& operator-=(difference_type n);
Derived operator-(difference_type n) const;
};
// Comparison operators
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type // exposition
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operator ==(iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator !=(iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator < (iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator < =(iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator > (iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator > =(iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator > =(iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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// Iterator difference
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template < class Dr1, class V1, class TC1, class R1, class D1,
class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable< Dr1, Dr2, bool> ::type
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operator -(iterator_facade< Dr1, V1, TC1, R1, D1> const& lhs,
iterator_facade< Dr2, V2, TC2, R2, D2> const& rhs);
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// Iterator addition
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template < class Derived, class V, class TC, class R, class D>
Derived operator+ (iterator_facade< Derived, V, TC, R, D> const& ,
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typename Derived::difference_type n)
< / pre >
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< a class = "target" id = "iterator-category" name = "iterator-category" > < / a > < p > The < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > member of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > is< / p >
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< pre class = "literal-block" >
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< em > iterator-category< / em > (CategoryOrTraversal, value_type, reference)
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< / pre >
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< p > where < em > iterator-category< / em > is defined as follows:< / p >
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< a class = "target" id = "id11" name = "id11" > < / a > < pre class = "literal-block" >
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< em > iterator-category< / em > (C,R,V) :=
if (C is convertible to std::input_iterator_tag
|| C is convertible to std::output_iterator_tag
)
return C
else if (C is not convertible to incrementable_traversal_tag)
< em > the program is ill-formed< / em >
else return a type X satisfying the following two constraints:
1. X is convertible to X1, and not to any more-derived
type, where X1 is defined by:
if (R is a reference type
& & C is convertible to forward_traversal_tag)
{
if (C is convertible to random_access_traversal_tag)
X1 = random_access_iterator_tag
else if (C is convertible to bidirectional_traversal_tag)
X1 = bidirectional_iterator_tag
else
X1 = forward_iterator_tag
}
else
{
if (C is convertible to single_pass_traversal_tag
& & R is convertible to V)
X1 = input_iterator_tag
else
X1 = C
}
2. < a class = "reference" href = "new-iter-concepts.html#category-to-traversal" > < em > category-to-traversal< / em > < / a > (X) is convertible to the most
derived traversal tag type to which X is also
convertible, and not to any more-derived traversal tag
type.
< / pre >
< p > [Note: the intention is to allow < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > to be one of
the five original category tags when convertibility to one of the
traversal tags would add no information]< / p >
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<!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
<!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
< p > If < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt > is < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > then
< tt class = "literal" > < span class = "pre" > iterator_traversal< Derived> ::type< / span > < / tt > is convertible to the most
derived standard traversal tag type to which
< tt class = "literal" > < span class = "pre" > iterator_traversal< Iterator> ::type< / span > < / tt > is also convertible, and not to
any more-derived traversal tag type. Otherwise
< tt class = "literal" > < span class = "pre" > iterator_traversal< Derived> ::type< / span > < / tt > is convertible to the most
derived standard traversal tag type to which < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt >
is also convertible, and not to any more-derived traversal tag type.< / p >
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< p > The < tt class = "literal" > < span class = "pre" > enable_if_interoperable< / span > < / tt > template used above is for exposition
purposes. The member operators should be only be in an overload set
provided the derived types < tt class = "literal" > < span class = "pre" > Dr1< / span > < / tt > and < tt class = "literal" > < span class = "pre" > Dr2< / span > < / tt > are interoperable,
meaning that at least one of the types is convertible to the other. The
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< tt class = "literal" > < span class = "pre" > enable_if_interoperable< / span > < / tt > approach uses SFINAE to take the operators
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out of the overload set when the types are not interoperable.
The operators should behave < em > as-if< / em > < tt class = "literal" > < span class = "pre" > enable_if_interoperable< / span > < / tt >
were defined to be:< / p >
< pre class = "literal-block" >
template < bool, typename> enable_if_interoperable_impl
{};
template < typename T> enable_if_interoperable_impl< true,T>
{ typedef T type; };
template< typename Dr1, typename Dr2, typename T>
struct enable_if_interoperable
: enable_if_interoperable_impl<
is_convertible< Dr1,Dr2> ::value || is_convertible< Dr2,Dr1> ::value
, T
>
{};
< / pre >
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< / div >
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< div class = "section" id = "iterator-facade-requirements" >
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< h3 > < a class = "toc-backref" href = "#id30" name = "iterator-facade-requirements" > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > Requirements< / a > < / h3 >
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< p > The following table describes the typical valid expressions on
< tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > 's < tt class = "literal" > < span class = "pre" > Derived< / span > < / tt > parameter, depending on the
iterator concept(s) it will model. The operations in the first
column must be made accessible to member functions of class
< tt class = "literal" > < span class = "pre" > iterator_core_access< / span > < / tt > .< / p >
< p > In the table below, < tt class = "literal" > < span class = "pre" > F< / span > < / tt > is < tt class = "literal" > < span class = "pre" > iterator_facade< X,V,C,R,D> < / span > < / tt > , < tt class = "literal" > < span class = "pre" > a< / span > < / tt > is an
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object of type < tt class = "literal" > < span class = "pre" > X< / span > < / tt > , < tt class = "literal" > < span class = "pre" > b< / span > < / tt > and < tt class = "literal" > < span class = "pre" > c< / span > < / tt > are objects of type < tt class = "literal" > < span class = "pre" > const< / span > < span class = "pre" > X< / span > < / tt > ,
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< tt class = "literal" > < span class = "pre" > n< / span > < / tt > is an object of < tt class = "literal" > < span class = "pre" > F::difference_type< / span > < / tt > , < tt class = "literal" > < span class = "pre" > y< / span > < / tt > is a constant
object of a single pass iterator type interoperable with < tt class = "literal" > < span class = "pre" > X< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > z< / span > < / tt >
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is a constant object of a random access traversal iterator type
interoperable with < tt class = "literal" > < span class = "pre" > X< / span > < / tt > .< / p >
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< a class = "target" id = "core-operations" name = "core-operations" > < / a > < div class = "topic" >
< p class = "topic-title" > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > Core Operations< / p >
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< table border class = "table" >
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< colgroup >
< col width = "19%" / >
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< col width = "21%" / >
< col width = "35%" / >
< col width = "25%" / >
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< / colgroup >
< thead valign = "bottom" >
< tr > < th > Expression< / th >
< th > Return Type< / th >
< th > Assertion/Note< / th >
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< th > Used to implement Iterator
Concept(s)< / th >
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< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > < tt class = "literal" > < span class = "pre" > c.dereference()< / span > < / tt > < / td >
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< td > < tt class = "literal" > < span class = "pre" > F::reference< / span > < / tt > < / td >
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< td > < / td >
< td > Readable Iterator, Writable
Iterator< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > c.equal(y)< / span > < / tt > < / td >
< td > convertible to bool< / td >
< td > true iff < tt class = "literal" > < span class = "pre" > c< / span > < / tt > and < tt class = "literal" > < span class = "pre" > y< / span > < / tt > refer to the
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same position.< / td >
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< td > Single Pass Iterator< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > a.increment()< / span > < / tt > < / td >
< td > unused< / td >
< td > < / td >
< td > Incrementable Iterator< / td >
< / tr >
< tr > < td > < tt class = "literal" > < span class = "pre" > a.decrement()< / span > < / tt > < / td >
< td > unused< / td >
< td > < / td >
< td > Bidirectional Traversal
Iterator< / td >
< / tr >
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< tr > < td > < tt class = "literal" > < span class = "pre" > a.advance(n)< / span > < / tt > < / td >
< td > unused< / td >
< td > < / td >
< td > Random Access Traversal
Iterator< / td >
< / tr >
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< tr > < td > < tt class = "literal" > < span class = "pre" > c.distance_to(z)< / span > < / tt > < / td >
< td > convertible to
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< tt class = "literal" > < span class = "pre" > F::difference_type< / span > < / tt > < / td >
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< td > equivalent to < tt class = "literal" > < span class = "pre" > distance(c,< / span > < span class = "pre" > X(z))< / span > < / tt > .< / td >
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< td > Random Access Traversal
Iterator< / td >
< / tr >
< / tbody >
< / table >
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< / div >
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< / div >
< div class = "section" id = "iterator-facade-operations" >
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< h3 > < a class = "toc-backref" href = "#id31" name = "iterator-facade-operations" > < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > operations< / a > < / h3 >
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< p > The operations in this section are described in terms of operations on
the core interface of < tt class = "literal" > < span class = "pre" > Derived< / span > < / tt > which may be inaccessible
(i.e. private). The implementation should access these operations
through member functions of class < tt class = "literal" > < span class = "pre" > iterator_core_access< / span > < / tt > .< / p >
< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > static_cast< Derived< / span > < span class = "pre" > const*> (this)-> dereference()< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > operator-> ()< / span > < span class = "pre" > const;< / span > < / tt > (see < a class = "reference" href = "#operator-arrow" > below< / a > )< / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < p class = "first" > If < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > is a reference type, an object
of type < tt class = "literal" > < span class = "pre" > pointer< / span > < / tt > equal to:< / p >
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< pre class = "literal-block" >
& static_cast< Derived const*> (this)-> dereference()
< / pre >
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< p class = "last" > Otherwise returns an object of unspecified type such that,
< tt class = "literal" > < span class = "pre" > (*static_cast< Derived< / span > < span class = "pre" > const*> (this))-> m< / span > < / tt > is equivalent to < tt class = "literal" > < span class = "pre" > (w< / span > < span class = "pre" > =< / span > < span class = "pre" > **static_cast< Derived< / span > < span class = "pre" > const*> (this),< / span >
< span class = "pre" > w.m)< / span > < / tt > for some temporary object < tt class = "literal" > < span class = "pre" > w< / span > < / tt > of type < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > .< / p >
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< / td >
< / tr >
< / tbody >
< / table >
< a class = "target" id = "brackets" name = "brackets" > < / a > < p > < em > unspecified< / em > < tt class = "literal" > < span class = "pre" > operator[](difference_type< / span > < span class = "pre" > n)< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > an object convertible to < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > . For constant
objects < tt class = "literal" > < span class = "pre" > v< / span > < / tt > of type < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > n< / span > < / tt > of type
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< tt class = "literal" > < span class = "pre" > difference_type< / span > < / tt > , < tt class = "literal" > < span class = "pre" > (*this)[n]< / span > < span class = "pre" > =< / span > < span class = "pre" > v< / span > < / tt > is equivalent to
< tt class = "literal" > < span class = "pre" > *(*this< / span > < span class = "pre" > +< / span > < span class = "pre" > n)< / span > < span class = "pre" > =< / span > < span class = "pre" > v< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > static_cast< value_type< / span >
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< span class = "pre" > const& > ((*this)[n])< / span > < / tt > is equivalent to
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< tt class = "literal" > < span class = "pre" > static_cast< value_type< / span > < span class = "pre" > const& > (*(*this< / span > < span class = "pre" > +< / span > < span class = "pre" > n))< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
static_cast< Derived*> (this)-> increment();
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return *static_cast< Derived*> (this);
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< / pre >
< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived< / span > < span class = "pre" > operator++(int);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
Derived tmp(static_cast< Derived const*> (this));
++*this;
return tmp;
< / pre >
< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
static_cast< Derived*> (this)-> decrement();
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return static_cast< Derived*> (this);
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< / pre >
< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived< / span > < span class = "pre" > operator--(int);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
Derived tmp(static_cast< Derived const*> (this));
--*this;
return tmp;
< / pre >
< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived& < / span > < span class = "pre" > operator+=(difference_type< / span > < span class = "pre" > n);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
static_cast< Derived*> (this)-> advance(n);
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return static_cast< Derived*> (this);
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< / pre >
< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived& < / span > < span class = "pre" > operator-=(difference_type< / span > < span class = "pre" > n);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
static_cast< Derived*> (this)-> advance(-n);
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return static_cast< Derived*> (this);
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< / pre >
< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Derived< / span > < span class = "pre" > operator-(difference_type< / span > < span class = "pre" > n)< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < pre class = "first last literal-block" >
Derived tmp(static_cast< Derived const*> (this));
return tmp -= n;
< / pre >
< / td >
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< / tr >
< / tbody >
< / table >
< / div >
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< / div >
< div class = "section" id = "iterator-adaptor-lib-iterator-adaptor" >
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< h2 > < a class = "toc-backref" href = "#id32" name = "iterator-adaptor-lib-iterator-adaptor" > Iterator adaptor [lib.iterator.adaptor]< / a > < / h2 >
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<!-- Version 1.1 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG. -->
<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
rights reserved -->
< p > Each specialization of the < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > class template is derived from
a specialization of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > . The core interface functions
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expected by < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > are implemented in terms of the
< tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > 's < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > template parameter. A class derived
from < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > typically redefines some of the core
interface functions to adapt the behavior of the < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > type.
Whether the derived class models any of the standard iterator concepts
depends on the operations supported by the < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > type and which
core interface functions of < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt > are redefined in the
< tt class = "literal" > < span class = "pre" > Derived< / span > < / tt > class.< / p >
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< div class = "section" id = "class-template-iterator-adaptor" >
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< h3 > < a class = "toc-backref" href = "#id33" name = "class-template-iterator-adaptor" > Class template < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > < / a > < / h3 >
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<!-- Version 1.4 of this ReStructuredText document corresponds to
n1530_, the paper accepted by the LWG for TR1. -->
<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003. All
rights reserved. -->
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< pre class = "literal-block" >
template <
class Derived
, class Base
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, class Value = use_default
, class CategoryOrTraversal = use_default
, class Reference = use_default
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, class Difference = use_default
>
class iterator_adaptor
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: public iterator_facade< Derived, < em > V< / em > , < em > C< / em > , < em > R< / em > , < em > D< / em > > // see < a class = "reference" href = "#requirements" > details< / a >
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{
friend class iterator_core_access;
public:
iterator_adaptor();
explicit iterator_adaptor(Base iter);
Base base() const;
protected:
Base const& base_reference() const;
Base& base_reference();
private: // Core iterator interface for iterator_facade.
typename iterator_adaptor::reference dereference() const;
template <
class OtherDerived, class OtherIterator, class V, class C, class R, class D
>
bool equal(iterator_adaptor< OtherDerived, OtherIterator, V, C, R, D> const& x) const;
void advance(typename iterator_adaptor::difference_type n);
void increment();
void decrement();
template <
class OtherDerived, class OtherIterator, class V, class C, class R, class D
>
typename iterator_adaptor::difference_type distance_to(
iterator_adaptor< OtherDerived, OtherIterator, V, C, R, D> const& y) const;
private:
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Base m_iterator; // exposition only
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};
< / pre >
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< a class = "target" id = "requirements" name = "requirements" > < / a > < / div >
< div class = "section" id = "iterator-adaptor-requirements" >
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< h3 > < a class = "toc-backref" href = "#id34" name = "iterator-adaptor-requirements" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > requirements< / a > < / h3 >
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< p > The < tt class = "literal" > < span class = "pre" > Derived< / span > < / tt > template argument must be a publicly derived from
< tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > .< / p >
< p > The < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > argument shall be Assignable and Copy Constructible.< / p >
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< a class = "target" id = "base-parameters" name = "base-parameters" > < / a > < / div >
< div class = "section" id = "iterator-adaptor-base-class-parameters" >
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< h3 > < a class = "toc-backref" href = "#id35" name = "iterator-adaptor-base-class-parameters" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > base class parameters< / a > < / h3 >
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< p > The < em > V< / em > , < em > C< / em > , < em > R< / em > , and < em > D< / em > parameters of the < tt class = "literal" > < span class = "pre" > iterator_facade< / span > < / tt >
used as a base class in the summary of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt >
above are defined as follows:< / p >
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< pre class = "literal-block" >
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< em > V< / em > = if (Value is use_default)
return iterator_traits< Base> ::value_type
else
return Value
< em > C< / em > = if (CategoryOrTraversal is use_default)
return iterator_traversal< Base> ::type
else
return CategoryOrTraversal
< em > R< / em > = if (Reference is use_default)
if (Value is use_default)
return iterator_traits< Base> ::reference
else
return Value&
else
return Reference
< em > D< / em > = if (Difference is use_default)
return iterator_traits< Base> ::difference_type
else
return Difference
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< / pre >
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< / div >
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< div class = "section" id = "iterator-adaptor-models" >
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< h3 > < a class = "toc-backref" href = "#id36" name = "iterator-adaptor-models" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > models< / a > < / h3 >
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< p > In order for < tt class = "literal" > < span class = "pre" > Derived< / span > < / tt > to model the iterator concepts corresponding
to < tt class = "literal" > < span class = "pre" > iterator_traits< Derived> ::iterator_category< / span > < / tt > , the expressions
involving < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > in the specifications of those private member
functions of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > that may be called by
< tt class = "literal" > < span class = "pre" > iterator_facade< Derived,< / span > < span class = "pre" > V,< / span > < span class = "pre" > C,< / span > < span class = "pre" > R,< / span > < span class = "pre" > D> < / span > < / tt > in evaluating any valid
expression involving < tt class = "literal" > < span class = "pre" > Derived< / span > < / tt > in those concepts' requirements.< / p >
<!-- The above is confusing and needs a rewrite. - JGS -->
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< / div >
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< div class = "section" id = "iterator-adaptor-public-operations" >
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< h3 > < a class = "toc-backref" href = "#id37" name = "iterator-adaptor-public-operations" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > public operations< / a > < / h3 >
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< p > < tt class = "literal" > < span class = "pre" > iterator_adaptor();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > The < tt class = "literal" > < span class = "pre" > Base< / span > < / tt > type must be Default Constructible.< / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > with
< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > default constructed.< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > explicit< / span > < span class = "pre" > iterator_adaptor(Base< / span > < span class = "pre" > iter);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > with
< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > copy constructed from < tt class = "literal" > < span class = "pre" > iter< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Base< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< / div >
< div class = "section" id = "iterator-adaptor-protected-member-functions" >
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< h3 > < a class = "toc-backref" href = "#id38" name = "iterator-adaptor-protected-member-functions" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > protected member functions< / a > < / h3 >
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< p > < tt class = "literal" > < span class = "pre" > Base< / span > < span class = "pre" > const& < / span > < span class = "pre" > base_reference()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > A const reference to < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Base& < / span > < span class = "pre" > base_reference();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > A non-const reference to < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
< / div >
< div class = "section" id = "iterator-adaptor-private-member-functions" >
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< h3 > < a class = "toc-backref" href = "#id39" name = "iterator-adaptor-private-member-functions" > < tt class = "literal" > < span class = "pre" > iterator_adaptor< / span > < / tt > private member functions< / a > < / h3 >
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< p > < tt class = "literal" > < span class = "pre" > typename< / span > < span class = "pre" > iterator_adaptor::reference< / span > < span class = "pre" > dereference()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template <
class OtherDerived, class OtherIterator, class V, class C, class R, class D
>
bool equal(iterator_adaptor< OtherDerived, OtherIterator, V, C, R, D> const& x) const;
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < span class = "pre" > ==< / span > < span class = "pre" > x.base()< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > void< / span > < span class = "pre" > advance(typename< / span > < span class = "pre" > iterator_adaptor::difference_type< / span > < span class = "pre" > n);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < span class = "pre" > +=< / span > < span class = "pre" > n;< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > void< / span > < span class = "pre" > increment();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > ++m_iterator;< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > void< / span > < span class = "pre" > decrement();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > --m_iterator;< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template <
class OtherDerived, class OtherIterator, class V, class C, class R, class D
>
typename iterator_adaptor::difference_type distance_to(
iterator_adaptor< OtherDerived, OtherIterator, V, C, R, D> const& y) const;
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > y.base()< / span > < span class = "pre" > -< / span > < span class = "pre" > m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< / div >
< / div >
< div class = "section" id = "specialized-adaptors-lib-iterator-special-adaptors" >
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< h2 > < a class = "toc-backref" href = "#id40" name = "specialized-adaptors-lib-iterator-special-adaptors" > Specialized adaptors [lib.iterator.special.adaptors]< / a > < / h2 >
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< p > The < tt class = "literal" > < span class = "pre" > enable_if_convertible< X,Y> ::type< / span > < / tt > expression used in
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this section is for exposition purposes. The converting constructors
for specialized adaptors should be only be in an overload set provided
that an object of type < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is implicitly convertible to an object of
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type < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > .
The signatures involving < tt class = "literal" > < span class = "pre" > enable_if_convertible< / span > < / tt > should behave
< em > as-if< / em > < tt class = "literal" > < span class = "pre" > enable_if_convertible< / span > < / tt > were defined to be:< / p >
< pre class = "literal-block" >
template < bool> enable_if_convertible_impl
{};
template < > enable_if_convertible_impl< true>
{ struct type; };
template< typename From, typename To>
struct enable_if_convertible
: enable_if_convertible_impl< is_convertible< From,To> ::value>
{};
< / pre >
< p > If an expression other than the default argument is used to supply
the value of a function parameter whose type is written in terms
of < tt class = "literal" > < span class = "pre" > enable_if_convertible< / span > < / tt > , the program is ill-formed, no
diagnostic required.< / p >
< p > [< em > Note:< / em > The < tt class = "literal" > < span class = "pre" > enable_if_convertible< / span > < / tt > approach uses SFINAE to
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take the constructor out of the overload set when the types are not
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implicitly convertible.
]< / p >
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< div class = "section" id = "indirect-iterator" >
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< h3 > < a class = "toc-backref" href = "#id41" name = "indirect-iterator" > Indirect iterator< / a > < / h3 >
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< p > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > adapts an iterator by applying an
< em > extra< / em > dereference inside of < tt class = "literal" > < span class = "pre" > operator*()< / span > < / tt > . For example, this
iterator adaptor makes it possible to view a container of pointers
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(e.g. < tt class = "literal" > < span class = "pre" > list< foo*> < / span > < / tt > ) as if it were a container of the pointed-to type
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(e.g. < tt class = "literal" > < span class = "pre" > list< foo> < / span > < / tt > ). < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > depends on two
auxiliary traits, < tt class = "literal" > < span class = "pre" > pointee< / span > < / tt > and < tt class = "literal" > < span class = "pre" > indirect_reference< / span > < / tt > , to
provide support for underlying iterators whose < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > is
not an iterator.< / p >
< div class = "section" id = "class-template-pointee" >
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< h4 > < a class = "toc-backref" href = "#id42" name = "class-template-pointee" > Class template < tt class = "literal" > < span class = "pre" > pointee< / span > < / tt > < / a > < / h4 >
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<!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
<!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
< pre class = "literal-block" >
template < class Dereferenceable>
struct pointee
{
typedef /* see below */ type;
};
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > For an object < tt class = "literal" > < span class = "pre" > x< / span > < / tt > of type < tt class = "literal" > < span class = "pre" > Dereferenceable< / span > < / tt > , < tt class = "literal" > < span class = "pre" > *x< / span > < / tt >
is well-formed. If < tt class = "literal" > < span class = "pre" > ++x< / span > < / tt > is ill-formed it shall neither be
ambiguous nor shall it violate access control, and
< tt class = "literal" > < span class = "pre" > Dereferenceable::element_type< / span > < / tt > shall be an accessible type.
Otherwise < tt class = "literal" > < span class = "pre" > iterator_traits< Dereferenceable> ::value_type< / span > < / tt > shall
be well formed. [Note: These requirements need not apply to
explicit or partial specializations of < tt class = "literal" > < span class = "pre" > pointee< / span > < / tt > ]< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > type< / span > < / tt > is determined according to the following algorithm, where
< tt class = "literal" > < span class = "pre" > x< / span > < / tt > is an object of type < tt class = "literal" > < span class = "pre" > Dereferenceable< / span > < / tt > :< / p >
< pre class = "literal-block" >
if ( ++x is ill-formed )
{
return ``Dereferenceable::element_type``
}
else if (``*x`` is a mutable reference to
std::iterator_traits< Dereferenceable> ::value_type)
{
return iterator_traits< Dereferenceable> ::value_type
}
else
{
return iterator_traits< Dereferenceable> ::value_type const
}
< / pre >
< / div >
< div class = "section" id = "class-template-indirect-reference" >
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< h4 > < a class = "toc-backref" href = "#id43" name = "class-template-indirect-reference" > Class template < tt class = "literal" > < span class = "pre" > indirect_reference< / span > < / tt > < / a > < / h4 >
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<!-- Copyright David Abrahams 2004. Use, modification and distribution is -->
<!-- subject to the Boost Software License, Version 1.0. (See accompanying -->
<!-- file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
< pre class = "literal-block" >
template < class Dereferenceable>
struct indirect_reference
{
typedef /* see below */ type;
};
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > For an object < tt class = "literal" > < span class = "pre" > x< / span > < / tt > of type < tt class = "literal" > < span class = "pre" > Dereferenceable< / span > < / tt > , < tt class = "literal" > < span class = "pre" > *x< / span > < / tt >
is well-formed. If < tt class = "literal" > < span class = "pre" > ++x< / span > < / tt > is ill-formed it shall neither be
ambiguous nor shall it violate access control, and
< tt class = "literal" > < span class = "pre" > pointee< Dereferenceable> ::type& < / span > < / tt > shall be well-formed.
Otherwise < tt class = "literal" > < span class = "pre" > iterator_traits< Dereferenceable> ::reference< / span > < / tt > shall
be well formed. [Note: These requirements need not apply to
explicit or partial specializations of < tt class = "literal" > < span class = "pre" > indirect_reference< / span > < / tt > ]< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > type< / span > < / tt > is determined according to the following algorithm, where
< tt class = "literal" > < span class = "pre" > x< / span > < / tt > is an object of type < tt class = "literal" > < span class = "pre" > Dereferenceable< / span > < / tt > :< / p >
< pre class = "literal-block" >
if ( ++x is ill-formed )
return ``pointee< Dereferenceable> ::type& ``
else
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std::iterator_traits< Dereferenceable> ::reference
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< / pre >
< / div >
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< div class = "section" id = "class-template-indirect-iterator" >
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< h4 > < a class = "toc-backref" href = "#id44" name = "class-template-indirect-iterator" > Class template < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > < / a > < / h4 >
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< pre class = "literal-block" >
template <
class Iterator
, class Value = use_default
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, class CategoryOrTraversal = use_default
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, class Reference = use_default
, class Difference = use_default
>
class indirect_iterator
{
public:
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typedef /* see below */ value_type;
typedef /* see below */ reference;
typedef /* see below */ pointer;
typedef /* see below */ difference_type;
typedef /* see below */ iterator_category;
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indirect_iterator();
indirect_iterator(Iterator x);
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template <
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class Iterator2, class Value2, class Category2
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, class Reference2, class Difference2
>
indirect_iterator(
indirect_iterator<
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Iterator2, Value2, Category2, Reference2, Difference2
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> const& y
, typename enable_if_convertible< Iterator2, Iterator> ::type* = 0 // exposition
);
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Iterator base() const;
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reference operator*() const;
indirect_iterator& operator++();
indirect_iterator& operator--();
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private:
Iterator m_iterator; // exposition
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};
< / pre >
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< p > The member types of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > are defined according to
the following pseudo-code, where < tt class = "literal" > < span class = "pre" > V< / span > < / tt > is
< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > < / p >
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< pre class = "literal-block" >
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if (Value is use_default) then
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typedef remove_const< pointee< V> ::type> ::type value_type;
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else
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typedef remove_const< Value> ::type value_type;
if (Reference is use_default) then
if (Value is use_default) then
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typedef indirect_reference< V> ::type reference;
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else
typedef Value& reference;
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else
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typedef Reference reference;
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if (Value is use_default) then
typedef pointee< V> ::type* pointer;
else
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typedef Value* pointer;
if (Difference is use_default)
typedef iterator_traits< Iterator> ::difference_type difference_type;
else
typedef Difference difference_type;
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if (CategoryOrTraversal is use_default)
typedef < a class = "reference" href = "#id11" > < em > iterator-category< / em > < / a > (
iterator_traversal< Iterator> ::type,``reference``,``value_type``
) iterator_category;
else
typedef < a class = "reference" href = "#id11" > < em > iterator-category< / em > < / a > (
CategoryOrTraversal,``reference``,``value_type``
) iterator_category;
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< / pre >
< / div >
< div class = "section" id = "indirect-iterator-requirements" >
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< h4 > < a class = "toc-backref" href = "#id45" name = "indirect-iterator-requirements" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > requirements< / a > < / h4 >
2004-01-14 05:16:27 +01:00
< p > The expression < tt class = "literal" > < span class = "pre" > *v< / span > < / tt > , where < tt class = "literal" > < span class = "pre" > v< / span > < / tt > is an object of
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< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > , shall be valid
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expression and convertible to < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > . < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > shall
model the traversal concept indicated by < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > .
< tt class = "literal" > < span class = "pre" > Value< / span > < / tt > , < tt class = "literal" > < span class = "pre" > Reference< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > Difference< / span > < / tt > shall be chosen so
that < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > , < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > difference_type< / span > < / tt > meet
the requirements indicated by < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > .< / p >
< p > [Note: there are further requirements on the
< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > if the < tt class = "literal" > < span class = "pre" > Value< / span > < / tt >
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parameter is not < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > , as implied by the algorithm for
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deducing the default for the < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > member.]< / p >
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< / div >
< div class = "section" id = "indirect-iterator-models" >
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< h4 > < a class = "toc-backref" href = "#id46" name = "indirect-iterator-models" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models< / a > < / h4 >
2004-01-14 18:04:04 +01:00
< p > In addition to the concepts indicated by < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt >
and by < tt class = "literal" > < span class = "pre" > iterator_traversal< indirect_iterator> ::type< / span > < / tt > , a
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specialization of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > models the following
concepts, Where < tt class = "literal" > < span class = "pre" > v< / span > < / tt > is an object of
< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > :< / p >
< blockquote >
< ul class = "simple" >
< li > Readable Iterator if < tt class = "literal" > < span class = "pre" > reference(*v)< / span > < / tt > is convertible to
< tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > .< / li >
< li > Writable Iterator if < tt class = "literal" > < span class = "pre" > reference(*v)< / span > < span class = "pre" > =< / span > < span class = "pre" > t< / span > < / tt > is a valid
expression (where < tt class = "literal" > < span class = "pre" > t< / span > < / tt > is an object of type
< tt class = "literal" > < span class = "pre" > indirect_iterator::value_type< / span > < / tt > )< / li >
< li > Lvalue Iterator if < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > is a reference type.< / li >
< / ul >
< / blockquote >
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< p > < tt class = "literal" > < span class = "pre" > indirect_iterator< X,V1,C1,R1,D1> < / span > < / tt > is interoperable with
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< tt class = "literal" > < span class = "pre" > indirect_iterator< Y,V2,C2,R2,D2> < / span > < / tt > if and only if < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is
interoperable with < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > .< / p >
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< / div >
< div class = "section" id = "indirect-iterator-operations" >
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< h4 > < a class = "toc-backref" href = "#id47" name = "indirect-iterator-operations" > < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > operations< / a > < / h4 >
2004-01-14 05:16:27 +01:00
< p > In addition to the operations required by the concepts described
above, specializations of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > provide the
following operations.< / p >
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< p > < tt class = "literal" > < span class = "pre" > indirect_iterator();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > must be Default Constructible.< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > with
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a default-constructed < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator(Iterator< / span > < span class = "pre" > x);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > with
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< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > copy constructed from < tt class = "literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template <
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class Iterator2, class Value2, unsigned Access, class Traversal
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, class Reference2, class Difference2
>
indirect_iterator(
indirect_iterator<
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Iterator2, Value2, Access, Traversal, Reference2, Difference2
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> const& y
, typename enable_if_convertible< Iterator2, Iterator> ::type* = 0 // exposition
);
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Iterator2< / span > < / tt > is implicitly convertible to < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > .< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > indirect_iterator< / span > < / tt > whose
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< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > subobject is constructed from < tt class = "literal" > < span class = "pre" > y.base()< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > **m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > ++m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > indirect_iterator& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > --m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< / div >
< / div >
< div class = "section" id = "reverse-iterator" >
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< h3 > < a class = "toc-backref" href = "#id48" name = "reverse-iterator" > Reverse iterator< / a > < / h3 >
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< p > The reverse iterator adaptor iterates through the adapted iterator
range in the opposite direction.< / p >
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< div class = "section" id = "class-template-reverse-iterator" >
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< h4 > < a class = "toc-backref" href = "#id49" name = "class-template-reverse-iterator" > Class template < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > < / a > < / h4 >
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< pre class = "literal-block" >
template < class Iterator>
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class reverse_iterator
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{
public:
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typedef iterator_traits< Iterator> ::value_type value_type;
typedef iterator_traits< Iterator> ::reference reference;
typedef iterator_traits< Iterator> ::pointer pointer;
typedef iterator_traits< Iterator> ::difference_type difference_type;
typedef /* see below */ iterator_category;
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reverse_iterator() {}
explicit reverse_iterator(Iterator x) ;
template< class OtherIterator>
reverse_iterator(
reverse_iterator< OtherIterator> const& r
, typename enable_if_convertible< OtherIterator, Iterator> ::type* = 0 // exposition
);
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Iterator base() const;
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reference operator*() const;
reverse_iterator& operator++();
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reverse_iterator& operator--();
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private:
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Iterator m_iterator; // exposition
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};
< / pre >
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< p > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models Random Access Traversal Iterator and Readable
Lvalue Iterator, then < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
< tt class = "literal" > < span class = "pre" > random_access_iterator_tag< / span > < / tt > . Otherwise, if
< tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models Bidirectional Traversal Iterator and Readable
Lvalue Iterator, then < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
< tt class = "literal" > < span class = "pre" > bidirectional_iterator_tag< / span > < / tt > . Otherwise, < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "literal" > < span class = "pre" > input_iterator_tag< / span > < / tt > .< / p >
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< / div >
< div class = "section" id = "reverse-iterator-requirements" >
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< h4 > < a class = "toc-backref" href = "#id50" name = "reverse-iterator-requirements" > < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > requirements< / a > < / h4 >
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< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > must be a model of Bidirectional Traversal Iterator.< / p >
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< / div >
< div class = "section" id = "reverse-iterator-models" >
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< h4 > < a class = "toc-backref" href = "#id51" name = "reverse-iterator-models" > < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > models< / a > < / h4 >
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< p > A specialization of < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > models the same iterator
traversal and iterator access concepts modeled by its < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt >
argument. In addition, it may model old iterator concepts
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specified in the following table:< / p >
< table border class = "table" >
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< colgroup >
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< col width = "53%" / >
< col width = "47%" / >
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< / colgroup >
< thead valign = "bottom" >
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< tr > < th > If < tt class = "literal" > < span class = "pre" > I< / span > < / tt > models< / th >
< th > then < tt class = "literal" > < span class = "pre" > reverse_iterator< I> < / span > < / tt > models< / th >
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< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > Readable Lvalue Iterator,
Bidirectional Traversal Iterator< / td >
< td > Bidirectional Iterator< / td >
< / tr >
< tr > < td > Writable Lvalue Iterator,
Bidirectional Traversal Iterator< / td >
< td > Mutable Bidirectional Iterator< / td >
< / tr >
< tr > < td > Readable Lvalue Iterator,
Random Access Traversal Iterator< / td >
< td > Random Access Iterator< / td >
< / tr >
< tr > < td > Writable Lvalue Iterator,
Random Access Traversal Iterator< / td >
< td > Mutable Random Access Iterator< / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reverse_iterator< X> < / span > < / tt > is interoperable with
< tt class = "literal" > < span class = "pre" > reverse_iterator< Y> < / span > < / tt > if and only if < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is interoperable with
< tt class = "literal" > < span class = "pre" > Y< / span > < / tt > .< / p >
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< / div >
< div class = "section" id = "reverse-iterator-operations" >
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< h4 > < a class = "toc-backref" href = "#id52" name = "reverse-iterator-operations" > < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > operations< / a > < / h4 >
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< p > In addition to the operations required by the concepts modeled by
< tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > , < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > provides the following
operations.< / p >
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< p > < tt class = "literal" > < span class = "pre" > reverse_iterator();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > must be Default Constructible.< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > with < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt >
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default constructed.< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > explicit< / span > < span class = "pre" > reverse_iterator(Iterator< / span > < span class = "pre" > x);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > with a
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< tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > constructed from < tt class = "literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template< class OtherIterator>
reverse_iterator(
reverse_iterator< OtherIterator> const& r
, typename enable_if_convertible< OtherIterator, Iterator> ::type* = 0 // exposition
);
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > OtherIterator< / span > < / tt > is implicitly convertible to < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > .< / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > reverse_iterator< / span > < / tt > that is a copy of < tt class = "literal" > < span class = "pre" > r< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < / td >
< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
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Iterator tmp = m_iterator;
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return *--tmp;
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< / pre >
< p > < tt class = "literal" > < span class = "pre" > reverse_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > --m_iterator< / span > < / tt > < / td >
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< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reverse_iterator& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > ++m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< / div >
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< / div >
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< div class = "section" id = "transform-iterator" >
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< h3 > < a class = "toc-backref" href = "#id53" name = "transform-iterator" > Transform iterator< / a > < / h3 >
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< p > The transform iterator adapts an iterator by modifying the
< tt class = "literal" > < span class = "pre" > operator*< / span > < / tt > to apply a function object to the result of
dereferencing the iterator and returning the result.< / p >
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< div class = "section" id = "class-template-transform-iterator" >
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< h4 > < a class = "toc-backref" href = "#id54" name = "class-template-transform-iterator" > Class template < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > < / a > < / h4 >
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<!-- Version 1.3 of this document was accepted for TR1 -->
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< pre class = "literal-block" >
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template < class UnaryFunction,
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class Iterator,
class Reference = use_default,
class Value = use_default>
class transform_iterator
{
public:
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typedef /* see below */ value_type;
typedef /* see below */ reference;
typedef /* see below */ pointer;
typedef iterator_traits< Iterator> ::difference_type difference_type;
typedef /* see below */ iterator_category;
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transform_iterator();
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transform_iterator(Iterator const& x, UnaryFunction f);
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template< class F2, class I2, class R2, class V2>
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transform_iterator(
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transform_iterator< F2, I2, R2, V2> const& t
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, typename enable_if_convertible< I2, Iterator> ::type* = 0 // exposition only
, typename enable_if_convertible< F2, UnaryFunction> ::type* = 0 // exposition only
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);
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Iterator base() const;
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UnaryFunction functor() const;
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reference operator*() const;
transform_iterator& operator++();
transform_iterator& operator--();
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private:
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Iterator m_iterator; // exposition only
UnaryFunction m_f; // exposition only
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};
< / pre >
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< p > If < tt class = "literal" > < span class = "pre" > Reference< / span > < / tt > is < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > then the < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > member of
< tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > is
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< tt class = "literal" > < span class = "pre" > result_of< UnaryFunction(iterator_traits< Iterator> ::reference)> ::type< / span > < / tt > .
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Otherwise, < tt class = "literal" > < span class = "pre" > reference< / span > < / tt > is < tt class = "literal" > < span class = "pre" > Reference< / span > < / tt > .< / p >
< p > If < tt class = "literal" > < span class = "pre" > Value< / span > < / tt > is < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > then the < tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > member is
< tt class = "literal" > < span class = "pre" > remove_cv< remove_reference< reference> < / span > < span class = "pre" > > ::type< / span > < / tt > . Otherwise,
< tt class = "literal" > < span class = "pre" > value_type< / span > < / tt > is < tt class = "literal" > < span class = "pre" > Value< / span > < / tt > .< / p >
< p > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models Readable Lvalue Iterator and if < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt >
models Random Access Traversal Iterator, then < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "literal" > < span class = "pre" > random_access_iterator_tag< / span > < / tt > . Otherwise, if
< tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models Bidirectional Traversal Iterator, then
< tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
< tt class = "literal" > < span class = "pre" > bidirectional_iterator_tag< / span > < / tt > . Otherwise < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "literal" > < span class = "pre" > forward_iterator_tag< / span > < / tt > . If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > does not
model Readable Lvalue Iterator then < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "literal" > < span class = "pre" > input_iterator_tag< / span > < / tt > .< / p >
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< / div >
< div class = "section" id = "transform-iterator-requirements" >
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< h4 > < a class = "toc-backref" href = "#id55" name = "transform-iterator-requirements" > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > requirements< / a > < / h4 >
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< p > The type < tt class = "literal" > < span class = "pre" > UnaryFunction< / span > < / tt > must be Assignable, Copy Constructible, and
the expression < tt class = "literal" > < span class = "pre" > f(*i)< / span > < / tt > must be valid where < tt class = "literal" > < span class = "pre" > f< / span > < / tt > is an object of
type < tt class = "literal" > < span class = "pre" > UnaryFunction< / span > < / tt > , < tt class = "literal" > < span class = "pre" > i< / span > < / tt > is an object of type < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > , and
where the type of < tt class = "literal" > < span class = "pre" > f(*i)< / span > < / tt > must be
< tt class = "literal" > < span class = "pre" > result_of< UnaryFunction(iterator_traits< Iterator> ::reference)> ::type< / span > < / tt > .< / p >
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< p > The argument < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > shall model Readable Iterator.< / p >
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< / div >
< div class = "section" id = "transform-iterator-models" >
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< h4 > < a class = "toc-backref" href = "#id56" name = "transform-iterator-models" > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > models< / a > < / h4 >
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< p > The resulting < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > models the most refined of the
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following options that is also modeled by < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > .< / p >
< blockquote >
< ul class = "simple" >
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< li > Writable Lvalue Iterator if < tt class = "literal" > < span class = "pre" > transform_iterator::reference< / span > < / tt > is a non-const reference.< / li >
< li > Readable Lvalue Iterator if < tt class = "literal" > < span class = "pre" > transform_iterator::reference< / span > < / tt > is a const reference.< / li >
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< li > Readable Iterator otherwise.< / li >
< / ul >
< / blockquote >
< p > The < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > models the most refined standard traversal
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concept that is modeled by the < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument.< / p >
< p > If < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > is a model of Readable Lvalue Iterator then
it models the following original iterator concepts depending on what
the < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument models.< / p >
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< table border class = "table" >
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< colgroup >
< col width = "51%" / >
< col width = "49%" / >
< / colgroup >
< thead valign = "bottom" >
< tr > < th > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models< / th >
< th > then < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models< / th >
< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > Single Pass Iterator< / td >
< td > Input Iterator< / td >
< / tr >
< tr > < td > Forward Traversal Iterator< / td >
< td > Forward Iterator< / td >
< / tr >
< tr > < td > Bidirectional Traversal Iterator< / td >
< td > Bidirectional Iterator< / td >
< / tr >
< tr > < td > Random Access Traversal Iterator< / td >
< td > Random Access Iterator< / td >
< / tr >
< / tbody >
< / table >
< p > If < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > models Writable Lvalue Iterator then it is a
mutable iterator (as defined in the old iterator requirements).< / p >
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< p > < tt class = "literal" > < span class = "pre" > transform_iterator< F1,< / span > < span class = "pre" > X,< / span > < span class = "pre" > R1,< / span > < span class = "pre" > V1> < / span > < / tt > is interoperable with
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< tt class = "literal" > < span class = "pre" > transform_iterator< F2,< / span > < span class = "pre" > Y,< / span > < span class = "pre" > R2,< / span > < span class = "pre" > V2> < / span > < / tt > if and only if < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is
interoperable with < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > .< / p >
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< / div >
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< div class = "section" id = "transform-iterator-operations" >
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< h4 > < a class = "toc-backref" href = "#id57" name = "transform-iterator-operations" > < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > operations< / a > < / h4 >
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< p > In addition to the operations required by the concepts modeled by
< tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > , < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > provides the following
operations.< / p >
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< p > < tt class = "literal" > < span class = "pre" > transform_iterator();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > with < tt class = "literal" > < span class = "pre" > m_f< / span > < / tt >
and < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > default constructed.< / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > transform_iterator(Iterator< / span > < span class = "pre" > const& < / span > < span class = "pre" > x,< / span > < span class = "pre" > UnaryFunction< / span > < span class = "pre" > f);< / span > < / tt > < / p >
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< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > with < tt class = "literal" > < span class = "pre" > m_f< / span > < / tt >
initialized to < tt class = "literal" > < span class = "pre" > f< / span > < / tt > and < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > initialized to < tt class = "literal" > < span class = "pre" > x< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template< class OtherIterator, class R2, class V2>
transform_iterator(
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transform_iterator< UnaryFunction, OtherIterator, R2, V2> const& t
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, typename enable_if_convertible< OtherIterator, Iterator> ::type* = 0 // exposition
);
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > transform_iterator< / span > < / tt > that is a copy of < tt class = "literal" > < span class = "pre" > t< / span > < / tt > .< / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > OtherIterator< / span > < / tt > is implicitly convertible to < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > .< / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > UnaryFunction< / span > < span class = "pre" > functor()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
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< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_f< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
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< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_f(*m_iterator)< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > transform_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > ++m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > transform_iterator& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > --m_iterator< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< / div >
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< / div >
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< div class = "section" id = "filter-iterator" >
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< h3 > < a class = "toc-backref" href = "#id58" name = "filter-iterator" > Filter iterator< / a > < / h3 >
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< p > The filter iterator adaptor creates a view of an iterator range in
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which some elements of the range are skipped. A predicate function
object controls which elements are skipped. When the predicate is
applied to an element, if it returns < tt class = "literal" > < span class = "pre" > true< / span > < / tt > then the element is
retained and if it returns < tt class = "literal" > < span class = "pre" > false< / span > < / tt > then the element is skipped
over. When skipping over elements, it is necessary for the filter
adaptor to know when to stop so as to avoid going past the end of the
underlying range. A filter iterator is therefore constructed with pair
of iterators indicating the range of elements in the unfiltered
sequence to be traversed.< / p >
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< div class = "section" id = "class-template-filter-iterator" >
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< h4 > < a class = "toc-backref" href = "#id59" name = "class-template-filter-iterator" > Class template < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > < / a > < / h4 >
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<!-- Copyright David Abrahams, Jeremy Siek, and Thomas Witt -->
<!-- 2004. Use, modification and distribution is subject to the Boost -->
<!-- Software License, Version 1.0. (See accompanying file -->
<!-- LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) -->
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< pre class = "literal-block" >
template < class Predicate, class Iterator>
class filter_iterator
{
public:
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typedef iterator_traits< Iterator> ::value_type value_type;
typedef iterator_traits< Iterator> ::reference reference;
typedef iterator_traits< Iterator> ::pointer pointer;
typedef iterator_traits< Iterator> ::difference_type difference_type;
typedef /* see below */ iterator_category;
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filter_iterator();
filter_iterator(Predicate f, Iterator x, Iterator end = Iterator());
filter_iterator(Iterator x, Iterator end = Iterator());
template< class OtherIterator>
filter_iterator(
filter_iterator< Predicate, OtherIterator> const& t
, typename enable_if_convertible< OtherIterator, Iterator> ::type* = 0 // exposition
);
Predicate predicate() const;
Iterator end() const;
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Iterator base() const;
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reference operator*() const;
filter_iterator& operator++();
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private:
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Predicate m_pred; // exposition only
Iterator m_iter; // exposition only
Iterator m_end; // exposition only
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};
< / pre >
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< p > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models Readable Lvalue Iterator and Forward Traversal
Iterator then < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
< tt class = "literal" > < span class = "pre" > std::forward_iterator_tag< / span > < / tt > . Otherwise < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is
convertible to < tt class = "literal" > < span class = "pre" > std::input_iterator_tag< / span > < / tt > .< / p >
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< / div >
< div class = "section" id = "filter-iterator-requirements" >
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< h4 > < a class = "toc-backref" href = "#id60" name = "filter-iterator-requirements" > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > requirements< / a > < / h4 >
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< p > The < tt class = "literal" > < span class = "pre" > Predicate< / span > < / tt > argument must be Assignable, Copy Constructible, and
the expression < tt class = "literal" > < span class = "pre" > p(x)< / span > < / tt > must be valid where < tt class = "literal" > < span class = "pre" > p< / span > < / tt > is an object of type
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< tt class = "literal" > < span class = "pre" > Predicate< / span > < / tt > , < tt class = "literal" > < span class = "pre" > x< / span > < / tt > is an object of type
< tt class = "literal" > < span class = "pre" > iterator_traits< Iterator> ::value_type< / span > < / tt > , and where the type of
< tt class = "literal" > < span class = "pre" > p(x)< / span > < / tt > must be convertible to < tt class = "literal" > < span class = "pre" > bool< / span > < / tt > .< / p >
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< p > The < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument shall meet the requirements of Readable
Iterator and Single Pass Iterator or it shall meet the requirements of
Input Iterator.< / p >
< / div >
< div class = "section" id = "filter-iterator-models" >
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< h4 > < a class = "toc-backref" href = "#id61" name = "filter-iterator-models" > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models< / a > < / h4 >
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< p > The concepts that < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models are dependent on which
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concepts the < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > argument models, as specified in the
following tables.< / p >
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< table border class = "table" >
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< colgroup >
< col width = "33%" / >
< col width = "67%" / >
< / colgroup >
< thead valign = "bottom" >
< tr > < th > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models< / th >
< th > then < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models< / th >
< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > Single Pass Iterator< / td >
< td > Single Pass Iterator< / td >
< / tr >
< tr > < td > Forward Traversal Iterator< / td >
< td > Forward Traversal Iterator< / td >
< / tr >
< / tbody >
< / table >
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< table border class = "table" >
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< colgroup >
< col width = "41%" / >
< col width = "59%" / >
< / colgroup >
< thead valign = "bottom" >
< tr > < th > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models< / th >
< th > then < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models< / th >
< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > Readable Iterator< / td >
< td > Readable Iterator< / td >
< / tr >
< tr > < td > Writable Iterator< / td >
< td > Writable Iterator< / td >
< / tr >
< tr > < td > Lvalue Iterator< / td >
< td > Lvalue Iterator< / td >
< / tr >
< / tbody >
< / table >
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< table border class = "table" >
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< colgroup >
< col width = "63%" / >
< col width = "38%" / >
< / colgroup >
< thead valign = "bottom" >
< tr > < th > If < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > models< / th >
< th > then < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models< / th >
< / tr >
< / thead >
< tbody valign = "top" >
< tr > < td > Readable Iterator, Single Pass Iterator< / td >
< td > Input Iterator< / td >
< / tr >
< tr > < td > Readable Lvalue Iterator, Forward Traversal Iterator< / td >
< td > Forward Iterator< / td >
< / tr >
< tr > < td > Writable Lvalue Iterator, Forward Traversal Iterator< / td >
< td > Mutable Forward Iterator< / td >
< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > filter_iterator< P1,< / span > < span class = "pre" > X> < / span > < / tt > is interoperable with < tt class = "literal" > < span class = "pre" > filter_iterator< P2,< / span > < span class = "pre" > Y> < / span > < / tt >
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if and only if < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is interoperable with < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > .< / p >
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< / div >
< div class = "section" id = "filter-iterator-operations" >
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< h4 > < a class = "toc-backref" href = "#id62" name = "filter-iterator-operations" > < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > operations< / a > < / h4 >
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< p > In addition to those operations required by the concepts that
< tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > models, < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > provides the following
operations.< / p >
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< p > < tt class = "literal" > < span class = "pre" > filter_iterator();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Predicate< / span > < / tt > and < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > must be Default Constructible.< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > a < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > whose``m_pred``, < tt class = "literal" > < span class = "pre" > m_iter< / span > < / tt > , and < tt class = "literal" > < span class = "pre" > m_end< / span > < / tt >
members are a default constructed.< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > filter_iterator(Predicate< / span > < span class = "pre" > f,< / span > < span class = "pre" > Iterator< / span > < span class = "pre" > x,< / span > < span class = "pre" > Iterator< / span > < span class = "pre" > end< / span > < span class = "pre" > =< / span > < span class = "pre" > Iterator());< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > A < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > where < tt class = "literal" > < span class = "pre" > m_iter< / span > < / tt > is either
the first position in the range < tt class = "literal" > < span class = "pre" > [x,end)< / span > < / tt > such that < tt class = "literal" > < span class = "pre" > f(*m_iter)< / span > < span class = "pre" > ==< / span > < span class = "pre" > true< / span > < / tt >
or else``m_iter == end``. The member < tt class = "literal" > < span class = "pre" > m_pred< / span > < / tt > is constructed from
< tt class = "literal" > < span class = "pre" > f< / span > < / tt > and < tt class = "literal" > < span class = "pre" > m_end< / span > < / tt > from < tt class = "literal" > < span class = "pre" > end< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > filter_iterator(Iterator< / span > < span class = "pre" > x,< / span > < span class = "pre" > Iterator< / span > < span class = "pre" > end< / span > < span class = "pre" > =< / span > < span class = "pre" > Iterator());< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Predicate< / span > < / tt > must be Default Constructible and
< tt class = "literal" > < span class = "pre" > Predicate< / span > < / tt > is a class type (not a function pointer).< / td >
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< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > A < tt class = "literal" > < span class = "pre" > filter_iterator< / span > < / tt > where < tt class = "literal" > < span class = "pre" > m_iter< / span > < / tt > is either
the first position in the range < tt class = "literal" > < span class = "pre" > [x,end)< / span > < / tt > such that < tt class = "literal" > < span class = "pre" > m_pred(*m_iter)< / span > < span class = "pre" > ==< / span > < span class = "pre" > true< / span > < / tt >
or else``m_iter == end``. The member < tt class = "literal" > < span class = "pre" > m_pred< / span > < / tt > is default constructed.< / td >
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< / tr >
< / tbody >
< / table >
< pre class = "literal-block" >
template < class OtherIterator>
filter_iterator(
filter_iterator< Predicate, OtherIterator> const& t
, typename enable_if_convertible< OtherIterator, Iterator> ::type* = 0 // exposition
);``
< / pre >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > OtherIterator< / span > < / tt > is implicitly convertible to < tt class = "literal" > < span class = "pre" > Iterator< / span > < / tt > .< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > A filter iterator whose members are copied from < tt class = "literal" > < span class = "pre" > t< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Predicate< / span > < span class = "pre" > predicate()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_pred< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > end()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_end< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Iterator< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_iterator< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *m_iter< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > filter_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > Increments < tt class = "literal" > < span class = "pre" > m_iter< / span > < / tt > and then continues to
increment < tt class = "literal" > < span class = "pre" > m_iter< / span > < / tt > until either < tt class = "literal" > < span class = "pre" > m_iter< / span > < span class = "pre" > ==< / span > < span class = "pre" > m_end< / span > < / tt >
or < tt class = "literal" > < span class = "pre" > m_pred(*m_iter)< / span > < span class = "pre" > ==< / span > < span class = "pre" > true< / span > < / tt > .< / td >
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< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
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< / div >
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< / div >
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< div class = "section" id = "counting-iterator" >
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< h3 > < a class = "toc-backref" href = "#id63" name = "counting-iterator" > Counting iterator< / a > < / h3 >
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< p > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > adapts an object by adding an < tt class = "literal" > < span class = "pre" > operator*< / span > < / tt > that
returns the current value of the object. All other iterator operations
are forwarded to the adapted object.< / p >
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< div class = "section" id = "class-template-counting-iterator" >
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< h4 > < a class = "toc-backref" href = "#id64" name = "class-template-counting-iterator" > Class template < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > < / a > < / h4 >
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< pre class = "literal-block" >
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template <
class Incrementable
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, class CategoryOrTraversal = use_default
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, class Difference = use_default
>
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class counting_iterator
{
public:
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typedef Incrementable value_type;
typedef const Incrementable& reference;
typedef const Incrementable* pointer;
typedef /* see below */ difference_type;
typedef /* see below */ iterator_category;
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counting_iterator();
counting_iterator(counting_iterator const& rhs);
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explicit counting_iterator(Incrementable x);
Incrementable base() const;
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reference operator*() const;
counting_iterator& operator++();
counting_iterator& operator--();
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private:
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Incrementable m_inc; // exposition
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};
< / pre >
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< p > If the < tt class = "literal" > < span class = "pre" > Difference< / span > < / tt > argument is < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > then
< tt class = "literal" > < span class = "pre" > difference_type< / span > < / tt > is an unspecified signed integral
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type. Otherwise < tt class = "literal" > < span class = "pre" > difference_type< / span > < / tt > is < tt class = "literal" > < span class = "pre" > Difference< / span > < / tt > .< / p >
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< p > < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is determined according to the following
algorithm:< / p >
< pre class = "literal-block" >
if (CategoryOrTraversal is not use_default)
return CategoryOrTraversal
else if (numeric_limits< Incrementable> ::is_specialized)
return < a class = "reference" href = "#id11" > < em > iterator-category< / em > < / a > (
random_access_traversal_tag, Incrementable, const Incrementable& )
else
return < a class = "reference" href = "#id11" > < em > iterator-category< / em > < / a > (
iterator_traversal< Incrementable> ::type,
Incrementable, const Incrementable& )
< / pre >
< p > [< em > Note:< / em > implementers are encouraged to provide an implementation
of < tt class = "literal" > < span class = "pre" > operator-< / span > < / tt > and a default < tt class = "literal" > < span class = "pre" > difference_type< / span > < / tt > that avoid
overflows when < tt class = "literal" > < span class = "pre" > Incrementable< / span > < / tt > is a numeric type.]< / p >
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< / div >
< div class = "section" id = "counting-iterator-requirements" >
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< h4 > < a class = "toc-backref" href = "#id65" name = "counting-iterator-requirements" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > requirements< / a > < / h4 >
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< p > The < tt class = "literal" > < span class = "pre" > Incrementable< / span > < / tt > argument shall be Copy Constructible and Assignable.< / p >
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< p > If < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to < tt class = "literal" > < span class = "pre" > forward_iterator_tag< / span > < / tt >
or < tt class = "literal" > < span class = "pre" > forward_traversal_tag< / span > < / tt > , the following must be well-formed:< / p >
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< pre class = "literal-block" >
Incrementable i, j;
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++i; // pre-increment
i == j; // operator equal
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< / pre >
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< p > If < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
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< tt class = "literal" > < span class = "pre" > bidirectional_iterator_tag< / span > < / tt > or < tt class = "literal" > < span class = "pre" > bidirectional_traversal_tag< / span > < / tt > ,
the following expression must also be well-formed:< / p >
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< pre class = "literal-block" >
--i
< / pre >
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< p > If < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible to
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< tt class = "literal" > < span class = "pre" > random_access_iterator_tag< / span > < / tt > or < tt class = "literal" > < span class = "pre" > random_access_traversal_tag< / span > < / tt > ,
the following must must also be valid:< / p >
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< pre class = "literal-block" >
counting_iterator::difference_type n;
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i += n;
n = i - j;
i < j;
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< / pre >
< / div >
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< div class = "section" id = "counting-iterator-models" >
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< h4 > < a class = "toc-backref" href = "#id66" name = "counting-iterator-models" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > models< / a > < / h4 >
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< p > Specializations of < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > model Readable Lvalue
Iterator. In addition, they model the concepts corresponding to the
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iterator tags to which their < tt class = "literal" > < span class = "pre" > iterator_category< / span > < / tt > is convertible.
Also, if < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt > is not < tt class = "literal" > < span class = "pre" > use_default< / span > < / tt > then
< tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > models the concept corresponding to the iterator
tag < tt class = "literal" > < span class = "pre" > CategoryOrTraversal< / span > < / tt > . Otherwise, if
< tt class = "literal" > < span class = "pre" > numeric_limits< Incrementable> ::is_specialized< / span > < / tt > , then
< tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > models Random Access Traversal Iterator.
Otherwise, < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > models the same iterator traversal
concepts modeled by < tt class = "literal" > < span class = "pre" > Incrementable< / span > < / tt > .< / p >
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< p > < tt class = "literal" > < span class = "pre" > counting_iterator< X,C1,D1> < / span > < / tt > is interoperable with
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< tt class = "literal" > < span class = "pre" > counting_iterator< Y,C2,D2> < / span > < / tt > if and only if < tt class = "literal" > < span class = "pre" > X< / span > < / tt > is
interoperable with < tt class = "literal" > < span class = "pre" > Y< / span > < / tt > .< / p >
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< / div >
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< div class = "section" id = "counting-iterator-operations" >
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< h4 > < a class = "toc-backref" href = "#id67" name = "counting-iterator-operations" > < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > operations< / a > < / h4 >
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< p > In addition to the operations required by the concepts modeled by
< tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > , < tt class = "literal" > < span class = "pre" > counting_iterator< / span > < / tt > provides the following
operations.< / p >
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< p > < tt class = "literal" > < span class = "pre" > counting_iterator();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Requires:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > Incrementable< / span > < / tt > is Default Constructible.< / td >
< / tr >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > Default construct the member < tt class = "literal" > < span class = "pre" > m_inc< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > counting_iterator(counting_iterator< / span > < span class = "pre" > const& < / span > < span class = "pre" > rhs);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > Construct member < tt class = "literal" > < span class = "pre" > m_inc< / span > < / tt > from < tt class = "literal" > < span class = "pre" > rhs.m_inc< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > explicit< / span > < span class = "pre" > counting_iterator(Incrementable< / span > < span class = "pre" > x);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > Construct member < tt class = "literal" > < span class = "pre" > m_inc< / span > < / tt > from < tt class = "literal" > < span class = "pre" > x< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > reference< / span > < span class = "pre" > operator*()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_inc< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > counting_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > ++m_inc< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > counting_iterator& < / span > < span class = "pre" > operator--();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Effects:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > --m_inc< / span > < / tt > < / td >
< / tr >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > Incrementable< / span > < span class = "pre" > base()< / span > < span class = "pre" > const;< / span > < / tt > < / p >
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< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > m_inc< / span > < / tt > < / td >
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< / tr >
< / tbody >
< / table >
< / div >
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< / div >
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< div class = "section" id = "function-output-iterator" >
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< h3 > < a class = "toc-backref" href = "#id68" name = "function-output-iterator" > Function output iterator< / a > < / h3 >
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< p > The function output iterator adaptor makes it easier to create custom
output iterators. The adaptor takes a unary function and creates a
model of Output Iterator. Each item assigned to the output iterator is
passed as an argument to the unary function. The motivation for this
iterator is that creating a conforming output iterator is non-trivial,
particularly because the proper implementation usually requires a
proxy object.< / p >
< div class = "section" id = "class-template-function-output-iterator" >
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< h4 > < a class = "toc-backref" href = "#id69" name = "class-template-function-output-iterator" > Class template < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > < / a > < / h4 >
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< pre class = "literal-block" >
template < class UnaryFunction>
class function_output_iterator {
public:
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typedef std::output_iterator_tag iterator_category;
typedef void value_type;
typedef void difference_type;
typedef void pointer;
typedef void reference;
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explicit function_output_iterator(const UnaryFunction& f = UnaryFunction());
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/* see below */ operator*();
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function_output_iterator& operator++();
function_output_iterator& operator++(int);
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private:
UnaryFunction m_f; // exposition only
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};
< / pre >
< / div >
< div class = "section" id = "function-output-iterator-requirements" >
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< h4 > < a class = "toc-backref" href = "#id70" name = "function-output-iterator-requirements" > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > requirements< / a > < / h4 >
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< p > < tt class = "literal" > < span class = "pre" > UnaryFunction< / span > < / tt > must be Assignable and Copy Constructible.< / p >
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< / div >
< div class = "section" id = "function-output-iterator-models" >
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< h4 > < a class = "toc-backref" href = "#id71" name = "function-output-iterator-models" > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > models< / a > < / h4 >
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< p > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > is a model of the Writable and
Incrementable Iterator concepts.< / p >
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< / div >
< div class = "section" id = "function-output-iterator-operations" >
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< h4 > < a class = "toc-backref" href = "#id72" name = "function-output-iterator-operations" > < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > operations< / a > < / h4 >
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< p > < tt class = "literal" > < span class = "pre" > explicit< / span > < span class = "pre" > function_output_iterator(const< / span > < span class = "pre" > UnaryFunction& < / span > < span class = "pre" > f< / span > < span class = "pre" > =< / span > < span class = "pre" > UnaryFunction());< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An instance of < tt class = "literal" > < span class = "pre" > function_output_iterator< / span > < / tt > with
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< tt class = "literal" > < span class = "pre" > m_f< / span > < / tt > constructed from < tt class = "literal" > < span class = "pre" > f< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
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< p > < tt class = "literal" > < span class = "pre" > operator*();< / span > < / tt > < / p >
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< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
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< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > An object < tt class = "literal" > < span class = "pre" > r< / span > < / tt > of unspecified type such that < tt class = "literal" > < span class = "pre" > r< / span > < span class = "pre" > =< / span > < span class = "pre" > t< / span > < / tt >
is equivalent to < tt class = "literal" > < span class = "pre" > m_f(t)< / span > < / tt > for all < tt class = "literal" > < span class = "pre" > t< / span > < / tt > .< / td >
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< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > function_output_iterator& < / span > < span class = "pre" > operator++();< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
< p > < tt class = "literal" > < span class = "pre" > function_output_iterator& < / span > < span class = "pre" > operator++(int);< / span > < / tt > < / p >
< table class = "field-list" frame = "void" rules = "none" >
< col class = "field-name" / >
< col class = "field-body" / >
< tbody valign = "top" >
< tr class = "field" > < th class = "field-name" > Returns:< / th > < td class = "field-body" > < tt class = "literal" > < span class = "pre" > *this< / span > < / tt > < / td >
< / tr >
< / tbody >
< / table >
<!-- LocalWords: Abrahams Siek Witt istream ostream iter MTL strided interoperate
LocalWords: CRTP metafunctions inlining lvalue JGS incrementable BGL LEDA cv
LocalWords: GraphBase struct ptrdiff UnaryFunction const int typename bool pp
LocalWords: lhs rhs SFINAE markup iff tmp OtherDerived OtherIterator DWA foo
LocalWords: dereferenceable subobject AdaptableUnaryFunction impl pre ifdef'd
LocalWords: OtherIncrementable Coplien -->
< / div >
< / div >
< / div >
< / div >
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< / div >
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< hr class = "footer" / >
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< div class = "footer" >
< a class = "reference" href = "facade-and-adaptor.rst" > View document source< / a > .
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