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std::experimental::ranges::value_type

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< cpp‎ | experimental‎ | ranges
 
 
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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.

Contents

[edit] Helper alias template

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

[edit] 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.

[edit] Example

[edit] See also

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