25 Iterators library [iterators]

25.3 Iterator requirements [iterator.requirements]

25.3.4 Iterator concepts [iterator.concepts]

25.3.4.1 General [iterator.concepts.general]

1
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For a type I, let ITER_TRAITS(I) denote the type I if iterator_traits<I> names a specialization generated from the primary template.
Otherwise, ITER_TRAITS(I) denotes iterator_traits<I>.
  • (1.1)
    If the qualified-id ITER_TRAITS(I)​::​iterator_concept is valid and names a type, then ITER_CONCEPT(I) denotes that type.
  • (1.2)
    Otherwise, if the qualified-id ITER_TRAITS(I)​​::​iterator_category is valid and names a type, then ITER_CONCEPT(I) denotes that type.
  • (1.3)
    Otherwise, if iterator_traits<I> names a specialization generated from the primary template, then ITER_CONCEPT(I) denotes random_access_iterator_tag.
  • (1.4)
    Otherwise, ITER_CONCEPT(I) does not denote a type.
2
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[Note 1: 
ITER_TRAITS enables independent syntactic determination of an iterator's category and concept.
— end note]
[Example 1: 
struct I { using value_type = int; using difference_type = int; int operator*() const; I& operator++(); I operator++(int); I& operator--(); I operator--(int); bool operator==(I) const; }; iterator_traits<I>​::​iterator_category denotes input_iterator_tag, and ITER_CONCEPT(I) denotes random_access_iterator_tag.
— end example]