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[section:traits Iterator Traits]
`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_.
[h2 Synopsis]
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;
};
[h2 Broken Compiler Notes]
Because of workarounds in Boost, you may find that these
[@../../mpl/doc/index.html#metafunctions 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
[@../../type_traits/index.html#transformations 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.
[endsect]
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