/Src/Dependencies/Boost/libs/iterator/doc/iterator_traits.rst
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- .. Distributed under 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)
- +++++++++++++++++
- Iterator Traits
- +++++++++++++++++
- :Author: David Abrahams
- :Contact: dave@boost-consulting.com
- :organization: `Boost Consulting`_
- :date: $Date: 2008-03-23 08:45:55 +1100 (Sun, 23 Mar 2008) $
- :copyright: Copyright David Abrahams 2004.
- .. _`Boost Consulting`: http://www.boost-consulting.com
- :abstract: Header ``<boost/iterator/iterator_traits.hpp>`` provides
- the ability to access an iterator's associated types using
- MPL-compatible metafunctions_.
- .. _metafunctions: ../../mpl/doc/index.html#metafunctions
- Overview
- ========
- ``std::iterator_traits`` provides access to five associated types
- of any iterator: its ``value_type``, ``reference``, ``pointer``,
- ``iterator_category``, and ``difference_type``. Unfortunately,
- such a "multi-valued" traits template can be difficult to use in a
- metaprogramming context. ``<boost/iterator/iterator_traits.hpp>``
- provides access to these types using a standard metafunctions_.
- Summary
- =======
- Header ``<boost/iterator/iterator_traits.hpp>``::
- template <class Iterator>
- struct iterator_value
- {
- typedef typename
- std::iterator_traits<Iterator>::value_type
- type;
- };
- template <class Iterator>
- struct iterator_reference
- {
- typedef typename
- std::iterator_traits<Iterator>::reference
- type;
- };
- template <class Iterator>
- struct iterator_pointer
- {
- typedef typename
- std::iterator_traits<Iterator>::pointer
- type;
- };
- template <class Iterator>
- struct iterator_difference
- {
- typedef typename
- detail::iterator_traits<Iterator>::difference_type
- type;
- };
- template <class Iterator>
- struct iterator_category
- {
- typedef typename
- detail::iterator_traits<Iterator>::iterator_category
- type;
- };
- Broken Compiler Notes
- =====================
- Because of workarounds in Boost, you may find that these
- metafunctions_ actually work better than the facilities provided by
- your compiler's standard library.
- On compilers that don't support partial specialization, such as
- Microsoft Visual C++ 6.0 or 7.0, you may need to manually invoke
- BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION_ on the
- ``value_type`` of pointers that are passed to these metafunctions.
- Because of bugs in the implementation of GCC-2.9x, the name of
- ``iterator_category`` is changed to ``iterator_category_`` on that
- compiler. A macro, ``BOOST_ITERATOR_CATEGORY``, that expands to
- either ``iterator_category`` or ``iterator_category_``, as
- appropriate to the platform, is provided for portability.
- .. _BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION: ../../type_traits/index.html#transformations