std::experimental::ranges::ForwardIterator

< cpp‎ | experimental‎ | ranges
template < class I >

concept bool ForwardIterator =
  InputIterator<I> &&
  DerivedFrom<ranges::iterator_category_t<I>, ranges::forward_iterator_tag> &&
  Incrementable<I> &&

  Sentinel<I, I>;
 (ranges TS)

The concept ForwardIterator<I> refines InputIterator by adding equality comparison and the multi-pass guarantee.

The domain of == for forward iterators is that of iterators over the same underlying sequence, except that value-initialized iterators of the same type may be compared with each other and shall compare equal.

Pointers and references obtained from a forward iterator into a range [i, s) must remain valid while [i, s) continues to denote a range.

Let a and b be two deferenceable iterators of type I. ForwardIterator<I> is satisfied only if:

  • a == b implies ++a == ++b; and
  • The expression ([](X x){++x;}(a), *a) is equivalent to *a, i.e., incrementing a copy of a has no effect on the result of dereferencing a.

This is known as the multi-pass guarantee.

Notes

A forward iterator cannot be "stashing": it cannot return a reference to an object within itself, because such references would be invalidated by the destruction of the forward iterator.