std::experimental::ranges::value_type

 

C++

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Technical Specifications

 

Technical specifications

Filesystem library (filesystem TS)

Library fundamentals (library fundamentals TS)

Library fundamentals 2 (library fundamentals 2 TS)

Extensions for parallelism (parallelism TS)

Extensions for parallelism 2 (parallelism TS v2)

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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>
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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 > struct value_type { };	(1)
template< class T > struct value_type<T*>;	(2)
template< class I >   requires std::is_array<I>::value struct value_type<I> : value_type<std::decay_t<I>> { };	(3)
template< class T > struct value_type<const T> : value_type<std::decay_t<T>> { };	(4)
template <class T>   requires requires { typename T::value_type; } struct value_type<T>;	(5)
template <class T>   requires requires { typename T::element_type; } struct value_type<T>;	(6)

Computes the associated value type of the type I, if any. Users may specialize value_type for a program-defined type.

1) Primary template is an empty struct.

2) Specialization for pointers. If T is an object type, provides a member type type equal to std::remove_cv_t<T>. Otherwise, there is no member type.

3) Specialization for array types.

4) Specialization for const-qualified types.

5) Specialization for types that define a public and accessible member type value_type. If T::value_type is an object type, provides a member type type equal to T::value_type. Otherwise, there is no member type.

6) Specialization for types that define a public and accessible member type element_type (e.g., std::shared_ptr). If T::element_type is an object type, provides a member type type equal to std::remove_cv_t<typename T::element_type>. Otherwise, there is no member type.

Helper alias template

template< class T > using value_type_t = typename ranges::value_type<T>::type;		(ranges TS)

Notes

If a type contains both a value_type member and a element_type member, then the specializations (5) and (6) are ambiguous.

value_type is intended for use with Readable types such as iterators. It is not intended for use with ranges.

See also

Readable	specifies that a type is readable by applying operator * (concept)
iterator_traits	compatibility traits class that collects an iterator’s associated types (alias template)