std::experimental::ranges::ForwardIterator - cppreference.com (original) (raw)

| | | | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | ----------- | | 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 dereferenceable 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.

[edit] 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.