std::experimental::ranges::ForwardIterator

 

C++

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Concepts library (C++20)

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Technical Specifications

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals 2 TS)

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Extensions for parallelism 2 (parallelism TS v2)

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Ranges

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Iterators library

Iterator concepts
Readable Writable WeaklyIncrementable Incrementable	Iterator Sentinel SizedSentinel	InputIterator ForwardIterator BidirectionalIterator RandomAccessIterator	OutputIterator
Indirect callable concepts
IndirectUnaryInvocableIndirectRegularUnaryInvocable	IndirectUnaryPredicate	IndirectRelation	IndirectStrictWeakOrder
Common algorithm requirements
IndirectlyMovable IndirectlyMovableStorable	IndirectlyCopyable IndirectlyCopyableStorable	IndirectlySwappable IndirectlyComparable	Permutable Mergeable Sortable
Concept utilities
indirect_result_of	projected
Iterator utilities and operations
iter_move iter_swap	advance distance	next prev
Iterator traits
difference_type value_type reference_trvalue_reference_titer_common_reference_t iterator_category	input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tag	ranges::iterator_traits std::iterator_traits<InputIterator>std::iterator_traits<OutputIterator>
Iterator adaptors
reverse_iterator move_iterator move_sentinel	back_insert_iterator front_insert_iterator insert_iterator	common_iterator counted_iterator default_sentinel	danglingsafe_iterator_t unreachable
Stream iterators
istream_iterator	ostream_iterator	istreambuf_iterator	ostreambuf_iterator

 

Defined in header <experimental/ranges/iterator>
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.