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Forward Traversal Concept
.........................
A class or built-in type ``X`` models the *Forward Traversal*
concept if, in addition to ``X`` meeting the requirements of Default
Constructible and Single Pass Iterator, the following expressions are
valid and respect the stated semantics.
+--------------------------------------------------------------------------------------------------------+
|Forward Traversal Iterator Requirements (in addition to Default Constructible and Single Pass Iterator) |
+---------------------------------------+-----------------------------------+----------------------------+
|Expression |Return Type |Assertion/Note |
+=======================================+===================================+============================+
|``X u;`` |``X&`` |note: ``u`` may have a |
| | |singular value. |
+---------------------------------------+-----------------------------------+----------------------------+
|``++r`` |``X&`` |``r == s`` and ``r`` is |
| | |dereferenceable implies |
| | |``++r == ++s.`` |
+---------------------------------------+-----------------------------------+----------------------------+
|``iterator_traits<X>::difference_type``|A signed integral type representing| |
| |the distance between iterators | |
| | | |
+---------------------------------------+-----------------------------------+----------------------------+
|``iterator_traversal<X>::type`` |Convertible to | |
| |``forward_traversal_tag`` | |
+---------------------------------------+-----------------------------------+----------------------------+
|
