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72 lines
2.0 KiB
Plaintext
72 lines
2.0 KiB
Plaintext
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[section:traits Iterator Traits]
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`std::iterator_traits` provides access to five associated types
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of any iterator: its `value_type`, `reference`, `pointer`,
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`iterator_category`, and `difference_type`. Unfortunately,
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such a "multi-valued" traits template can be difficult to use in a
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metaprogramming context. `<boost/iterator/iterator_traits.hpp>`
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provides access to these types using a standard metafunctions_.
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[h2 Synopsis]
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Header `<boost/iterator/iterator_traits.hpp>`:
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template <class Iterator>
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struct iterator_value
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{
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typedef typename
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std::iterator_traits<Iterator>::value_type
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type;
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};
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template <class Iterator>
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struct iterator_reference
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{
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typedef typename
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std::iterator_traits<Iterator>::reference
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type;
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};
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template <class Iterator>
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struct iterator_pointer
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{
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typedef typename
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std::iterator_traits<Iterator>::pointer
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type;
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};
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template <class Iterator>
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struct iterator_difference
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{
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typedef typename
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detail::iterator_traits<Iterator>::difference_type
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type;
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};
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template <class Iterator>
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struct iterator_category
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{
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typedef typename
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detail::iterator_traits<Iterator>::iterator_category
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type;
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};
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[h2 Broken Compiler Notes]
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Because of workarounds in Boost, you may find that these
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[@../../mpl/doc/index.html#metafunctions metafunctions] actually work better than the facilities provided by
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your compiler's standard library.
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On compilers that don't support partial specialization, such as
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Microsoft Visual C++ 6.0 or 7.0, you may need to manually invoke
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[@../../type_traits/index.html#transformations BOOST_BROKEN_COMPILER_TYPE_TRAITS_SPECIALIZATION] on the
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`value_type` of pointers that are passed to these metafunctions.
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Because of bugs in the implementation of GCC-2.9x, the name of
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`iterator_category` is changed to `iterator_category_` on that
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compiler. A macro, `BOOST_ITERATOR_CATEGORY`, that expands to
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either `iterator_category` or `iterator_category_`, as
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appropriate to the platform, is provided for portability.
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[endsect]
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