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std::indire...dable_traits(3) C++ Standard Libarystd::indire...dable_traits(3) NAME std::indirectly_readable_traits - std::indirectly_readable_traits Synopsis Defined in header <iterator> template< class I > (1) (since C++20) struct indirectly_readable_traits { }; template< class T > (2) (since C++20) struct indirectly_readable_traits<T*>; template< class I > requires std::is_array_v<I> (3) (since C++20) struct indirectly_readable_traits<I>; template< class T > struct indirectly_readable_traits<const T> : (4) (since C++20) indirectly_readable_traits<T> { }; template </*has-member-value-type*/ T> (5) (since C++20) struct indirectly_readable_traits<T>; template </*has-member-element-type*/ T> (6) (since C++20) struct indirectly_readable_traits<T>; template </*has-member-value-type*/ T> requires /*has-member-element-type*/<T> (7) (since C++20) struct indirectly_readable_traits<T> { }; template </*has-member-value-type*/ T> requires /*has-member-element-type*/<T> && std::same_as<std::remove_cv_t<typename T::element_type>, (8) (since C++20) std::remove_cv_t<typename T::value_type>> struct indirectly_readable_traits<T>; Computes the associated value type of the type I, if any. Users may specialize indirectly_readable_traits for a program-defined type. 1) Primary template has no member value_type. 2) Specialization for pointers. If T is an object type, provides a member type value_type equal to std::remove_cv_t<T>. Otherwise, there is no mem- ber value_type. 3) Specialization for array types. Provides a member type value_type equal to std::remove_cv_t<std::remove_extent_t<I>>. 4) Specialization for const-qualified types. 5) Specialization for types that define a public and accessible mem- ber type value_type (e.g., std::reverse_iterator). If T::value_type is an ob- ject type, provides a member type value_type equal to std::remove_cv_t<typename T::value_type>. Otherwise, there is no member value_type. 6) Specialization for types that define a public and accessible mem- ber type element_type (e.g., std::shared_ptr). If T::element_type is an ob- ject type, provides a member type value_type equal to std::remove_cv_t<typename T::ele- ment_type>. Otherwise, there is no member value_type. 7-8) Specialization for types that define public and accessible mem- ber types value_type and element_type (e.g., std::span). If both T::value_type and T::element_type are object types and they become the same type after removing cv-qualifiers on the top-level, provides a member type value_type equal to std::remove_cv_t<typename T::value_type>. Otherwise, there is no member value_type. Notes value_type is intended for use with indirectly_readable types such as iterators. It is not intended for use with ranges. Example This section is incomplete Reason: no example Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Cor- rect behavior specializations were ambiguous for LWG 3446 C++20 types containing a disam- biguating both value_type and element_type specializa- tion added member types LWG 3446 introduced hard error for LWG 3541 C++20 ambiguous cases that made re- sulting substitution value_type and element_type are failure different See also indirectly_readable specifies that a type is indirectly readable by applying (C++20) operator * (concept) iter_value_t iter_reference_t iter_const_reference_t iter_difference_t iter_rvalue_reference_t iter_common_reference_t computes the associated types of an iterator (C++20) (alias template) (C++20) (C++23) (C++20) (C++20) (C++20) iterator_traits provides uniform interface to the properties of an iterator (class template) http://cppreference.com 2022.07.31 std::indire...dable_traits(3)
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