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Jeremy Siek
2001-03-19 17:41:49 +00:00
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<head>
<title>Boost Iterator Traits</title>
</head>
<body>
<h1>Boost Iterator Traits</h1>
Header <tt><a href="../../boost/iterator_traits.hpp">boost/iterator_traits.hpp</a></tt>
<pre>
namespace boost {
template &lt;typename Iterator&gt;
struct iterator_traits
{
if (Iterator inherits from new_iterator_base) {
typedef typename Iterator::value_type value_type;
typedef typename Iterator::reference reference;
typedef typename Iterator::pointer pointer;
typedef typename Iterator::difference_type difference_type;
typedef typename Iterator::return_category return_category;
typedef typename Iterator::traversal_category traversal_category;
} else {
typedef std::iterator_traits&lt;Iterator&gt; OldTraits;
typedef typename OldTraits::value_type value_type;
typedef typename OldTraits::reference reference;
typedef typename OldTraits::pointer pointer;
typedef typename OldTraits::difference_type difference_type;
typedef typename OldTraits::iterator_category Cat;
<i>// Determine the traversal_category based on the old iterator_category</i>
if (Cat inherits from std::random_access_iterator_tag)
typedef boost::random_access_iterator_tag traversal_category;
else if (Cat inherits from std::bidirectional_iterator_tag)
typedef boost::bidirectional_iterator_tag traversal_category;
else if (Cat inherits from std::forward_iterator_tag)
typedef boost::forward_iterator_tag traversal_category;
else
typedef boost::single_pass_iterator_tag traversal_category;
<i>// Determine the return_category based on the old iterator_category and value_type</i>
if (Cat inherits from std::forward_iterator_tag)
if (is-const(T))
typedef boost::constant_lvalue_iterator_tag return_category;
else
typedef boost::mutable_lvalue_iterator_tag return_category;
else if (Cat inherits from std::input_iterator_tag)
typedef boost::readable_iterator_tag return_category;
else if (Cat inherits from std::output_iterator_tag)
typedef boost::writable_iterator_tag return_category;
else
typedef boost::error_iterator_tag return_category;
}
};
template &lt;typename T&gt;
struct iterator_traits&lt;T*&gt;
{
typedef T value_type;
typedef T&amp; reference;
typedef T* pointer;
typedef std::ptrdiff_t difference_type;
if (is-const(T))
typedef boost::constant_lvalue_iterator_tag return_category;
else
typedef boost::mutable_lvalue_iterator_tag return_category;
typedef boost::random_access_iterator_tag traversal_category;
};
}
</pre>
<hr>
<address><a href="mailto:jsiek@lsc.nd.edu">jeremy siek</a></address>
<!-- Created: Sun Mar 18 14:06:57 EST 2001 -->
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Last modified: Sun Mar 18 17:10:26 EST 2001
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