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]

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>.
  • If the qualified-id ITER_­TRAITS(I)​::​iterator_­concept is valid and names a type, then ITER_­CONCEPT(I) denotes that type.
  • Otherwise, if the qualified-id ITER_­TRAITS(I)​::​iterator_­category is valid and names a type, then ITER_­CONCEPT(I) denotes that type.
  • Otherwise, if iterator_­traits<I> names a specialization generated from the primary template, then ITER_­CONCEPT(I) denotes random_­access_­iterator_­tag.
  • Otherwise, ITER_­CONCEPT(I) does not denote a type.
[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]