442 lines
14 KiB
ReStructuredText
442 lines
14 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 1.3 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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.. parsed-literal::
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template <
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class Derived
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, class Value
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, class CategoryOrTraversal
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, class Reference = Value&
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, class Difference = ptrdiff_t
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>
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class iterator_facade {
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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 below__ \*/ iterator_category;
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reference operator\*() const;
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/* see below__ \*/ operator->() const;
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/* see below__ \*/ operator[](difference_type n) const;
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Derived& operator++();
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Derived operator++(int);
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Derived& operator--();
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Derived operator--(int);
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Derived& operator+=(difference_type n);
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Derived& operator-=(difference_type n);
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Derived operator-(difference_type n) const;
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protected:
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typedef iterator_facade iterator_facade\_;
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};
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// Comparison operators
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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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,
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class Dr2, class V2, class TC2, class R2, class D2>
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/* see below__ \*/
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operator-(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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// Iterator addition
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template <class Dr, class V, class TC, class R, class D>
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Derived operator+ (iterator_facade<Dr,V,TC,R,D> const&,
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typename Derived::difference_type n);
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template <class Dr, class V, class TC, class R, class D>
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Derived operator+ (typename Derived::difference_type n,
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iterator_facade<Dr,V,TC,R,D> const&);
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__ `iterator category`_
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__ `operator arrow`_
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__ brackets_
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__ minus_
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.. _`iterator category`:
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The ``iterator_category`` member of ``iterator_facade`` is
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.. parsed-literal::
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*iterator-category*\ (CategoryOrTraversal, reference, value_type)
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where *iterator-category* is defined as follows:
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.. include:: facade_iterator_category.rst
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The ``enable_if_interoperable`` template used above is for exposition
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purposes. The member operators should only be in an overload set
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provided the derived types ``Dr1`` and ``Dr2`` are interoperable,
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meaning that at least one of the types is convertible to the other. The
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``enable_if_interoperable`` approach uses SFINAE to take the operators
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out of the overload set when the types are not interoperable.
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The operators should behave *as-if* ``enable_if_interoperable``
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were defined to be::
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template <bool, typename> enable_if_interoperable_impl
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{};
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template <typename T> enable_if_interoperable_impl<true,T>
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{ typedef T type; };
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template<typename Dr1, typename Dr2, typename T>
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struct enable_if_interoperable
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: enable_if_interoperable_impl<
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is_convertible<Dr1,Dr2>::value || is_convertible<Dr2,Dr1>::value
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, T
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>
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{};
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``iterator_facade`` Requirements
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--------------------------------
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The following table describes the typical valid expressions on
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``iterator_facade``\ 's ``Derived`` parameter, depending on the
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iterator concept(s) it will model. The operations in the first
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column must be made accessible to member functions of class
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``iterator_core_access``. In addition,
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``static_cast<Derived*>(iterator_facade*)`` shall be well-formed.
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In the table below, ``F`` is ``iterator_facade<X,V,C,R,D>``, ``a`` is an
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object of type ``X``, ``b`` and ``c`` are objects of type ``const X``,
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``n`` is an object of ``F::difference_type``, ``y`` is a constant
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object of a single pass iterator type interoperable with ``X``, and ``z``
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is a constant object of a random access traversal iterator type
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interoperable with ``X``.
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.. _`core operations`:
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.. topic:: ``iterator_facade`` Core Operations
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+--------------------+----------------------+-------------------------+---------------------------+
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|Expression |Return Type |Assertion/Note |Used to implement Iterator |
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| | | |Concept(s) |
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+====================+======================+=========================+===========================+
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|``c.dereference()`` |``F::reference`` | |Readable Iterator, Writable|
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| | | |Iterator |
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+--------------------+----------------------+-------------------------+---------------------------+
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|``c.equal(y)`` |convertible to bool |true iff ``c`` and ``y`` |Single Pass Iterator |
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| | |refer to the same | |
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| | |position. | |
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+--------------------+----------------------+-------------------------+---------------------------+
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|``a.increment()`` |unused | |Incrementable Iterator |
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+--------------------+----------------------+-------------------------+---------------------------+
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|``a.decrement()`` |unused | |Bidirectional Traversal |
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| | | |Iterator |
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+--------------------+----------------------+-------------------------+---------------------------+
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|``a.advance(n)`` |unused | |Random Access Traversal |
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| | | |Iterator |
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+--------------------+----------------------+-------------------------+---------------------------+
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|``c.distance_to(z)``|convertible to |equivalent to |Random Access Traversal |
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| |``F::difference_type``|``distance(c, X(z))``. |Iterator |
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+--------------------+----------------------+-------------------------+---------------------------+
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``iterator_facade`` operations
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------------------------------
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The operations in this section are described in terms of operations on
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the core interface of ``Derived`` which may be inaccessible
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(i.e. private). The implementation should access these operations
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through member functions of class ``iterator_core_access``.
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``reference operator*() const;``
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:Returns: ``static_cast<Derived const*>(this)->dereference()``
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``operator->() const;`` (see below__)
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__ `operator arrow`_
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:Returns: If ``reference`` is a reference type, an object
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of type ``pointer`` equal to::
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&static_cast<Derived const*>(this)->dereference()
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Otherwise returns an object of unspecified type such that,
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``(*static_cast<Derived const*>(this))->m`` is equivalent to ``(w = **static_cast<Derived const*>(this),
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w.m)`` for some temporary object ``w`` of type ``value_type``.
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.. _brackets:
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*unspecified* ``operator[](difference_type n) const;``
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:Returns: an object convertible to ``value_type``. For constant
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objects ``v`` of type ``value_type``, and ``n`` of type
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``difference_type``, ``(*this)[n] = v`` is equivalent to
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``*(*this + n) = v``, and ``static_cast<value_type
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const&>((*this)[n])`` is equivalent to
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``static_cast<value_type const&>(*(*this + n))``
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``Derived& operator++();``
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:Effects:
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::
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static_cast<Derived*>(this)->increment();
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return *static_cast<Derived*>(this);
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``Derived operator++(int);``
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:Effects:
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::
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Derived tmp(static_cast<Derived const*>(this));
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++*this;
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return tmp;
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``Derived& operator--();``
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:Effects:
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::
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static_cast<Derived*>(this)->decrement();
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return *static_cast<Derived*>(this);
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``Derived operator--(int);``
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:Effects:
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::
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Derived tmp(static_cast<Derived const*>(this));
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--*this;
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return tmp;
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``Derived& operator+=(difference_type n);``
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:Effects:
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::
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static_cast<Derived*>(this)->advance(n);
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return *static_cast<Derived*>(this);
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``Derived& operator-=(difference_type n);``
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:Effects:
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::
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static_cast<Derived*>(this)->advance(-n);
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return *static_cast<Derived*>(this);
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``Derived operator-(difference_type n) const;``
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:Effects:
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::
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Derived tmp(static_cast<Derived const*>(this));
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return tmp -= n;
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::
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template <class Dr, class V, class TC, class R, class D>
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Derived operator+ (iterator_facade<Dr,V,TC,R,D> const&,
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typename Derived::difference_type n);
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template <class Dr, class V, class TC, class R, class D>
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Derived operator+ (typename Derived::difference_type n,
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iterator_facade<Dr,V,TC,R,D> const&);
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:Effects:
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::
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Derived tmp(static_cast<Derived const*>(this));
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return tmp += n;
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``((Dr1 const&)lhs).equal((Dr2 const&)rhs)``.
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Otherwise,
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``((Dr2 const&)rhs).equal((Dr1 const&)lhs)``.
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``!((Dr1 const&)lhs).equal((Dr2 const&)rhs)``.
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Otherwise,
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``!((Dr2 const&)rhs).equal((Dr1 const&)lhs)``.
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) < 0``.
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Otherwise,
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``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) > 0``.
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) <= 0``.
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Otherwise,
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``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) >= 0``.
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) > 0``.
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Otherwise,
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``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) < 0``.
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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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,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``((Dr1 const&)lhs).distance_to((Dr2 const&)rhs) >= 0``.
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Otherwise,
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``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs) <= 0``.
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.. _minus:
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::
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template <class Dr1, class V1, class TC1, class R1, class D1,
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class Dr2, class V2, class TC2, class R2, class D2>
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typename enable_if_interoperable<Dr1,Dr2,difference>::type
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operator -(iterator_facade<Dr1,V1,TC1,R1,D1> const& lhs,
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iterator_facade<Dr2,V2,TC2,R2,D2> const& rhs);
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:Return Type:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``difference`` shall be
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``iterator_traits<Dr1>::difference_type``.
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Otherwise
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``difference`` shall be ``iterator_traits<Dr2>::difference_type``
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:Returns:
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if ``is_convertible<Dr2,Dr1>::value``
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then
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``-((Dr1 const&)lhs).distance_to((Dr2 const&)rhs)``.
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Otherwise,
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``((Dr2 const&)rhs).distance_to((Dr1 const&)lhs)``.
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