44 lines
2.1 KiB
ReStructuredText
44 lines
2.1 KiB
ReStructuredText
.. Distributed under the Boost
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.. Software License, Version 1.0. (See accompanying
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.. file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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.. Version 1.2 of this ReStructuredText document corresponds to
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n1530_, the paper accepted by the LWG for TR1.
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.. Copyright David Abrahams, Jeremy Siek, and Thomas Witt 2003.
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The ``iterator_adaptor`` class template adapts some ``Base`` [#base]_
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type to create a new iterator. Instantiations of ``iterator_adaptor``
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are derived from a corresponding instantiation of ``iterator_facade``
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and implement the core behaviors in terms of the ``Base`` type. In
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essence, ``iterator_adaptor`` merely forwards all operations to an
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instance of the ``Base`` type, which it stores as a member.
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.. [#base] 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
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of the standard library, which provides a base() function to access
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the underlying iterator object of a ``reverse_iterator`` adaptor.
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The user of ``iterator_adaptor`` creates a class derived from an
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instantiation of ``iterator_adaptor`` and then selectively
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redefines some of the core member functions described in the
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``iterator_facade`` core requirements table. The ``Base`` type need
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not meet the full requirements for an iterator; it need only
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support the operations used by the core interface functions of
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``iterator_adaptor`` that have not been redefined in the user's
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derived class.
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Several of the template parameters of ``iterator_adaptor`` default
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to ``use_default``. This allows the
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user to make use of a default parameter even when she wants to
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specify a parameter later in the parameter list. Also, the
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defaults for the corresponding associated types are somewhat
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complicated, so metaprogramming is required to compute them, and
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``use_default`` can help to simplify the implementation. Finally,
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the identity of the ``use_default`` type is not left unspecified
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because specification helps to highlight that the ``Reference``
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template parameter may not always be identical to the iterator's
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``reference`` type, and will keep users from making mistakes based on
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that assumption.
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