std::indirectly_readable_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 >
   struct indirectly_readable_traits<T*> : (2) (since C++20)
       /* cond-value-type */<T> {};
   template< class I >
       requires std::is_array_v<I>
   struct indirectly_readable_traits<I>; (3) (since C++20)
   { using value_type =
   std::remove_cv_t<std::remove_extent_t<I>>; }
   template< class T >
   struct indirectly_readable_traits<const T> : (4) (since C++20)
       indirectly_readable_traits<T> {};
   template< /* has-member-value-type */ T >
   struct indirectly_readable_traits<T> : (5) (since C++20)
       /* cond-value-type */<typename T::value_type> {};
   template< /* has-member-element-type */ T >
   struct indirectly_readable_traits<T> : (6) (since C++20)
       /* cond-value-type */<typename T::element_type> {};
   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> :
       /* cond-value-type */<typename T::value_type> {};
   Helper classes and concepts
   template< class > (1) (exposition only*)
   struct /* cond-value-type */ {};
   template< class T >
       requires std::is_object_v<T> (2) (exposition only*)
   struct /* cond-value-type */ <T>
   { using value_type = std::remove_cv_t<T>; };
   template< class T >
   concept /* has-member-value-type */ = (3) (exposition only*)
       requires { typename T::value_type; };
   template< class T >
   concept /* has-member-element-type */ = (4) (exposition only*)
       requires { typename T::element_type; };
   Computes the associated value type of the template argument. If the associated value
   type exists, it is represented by the nested type value_type, otherwise value_type
   is not defined. A program may specialize indirectly_readable_traits for a
   program-defined type.

Explanation
   The specializations above can be informally described as below.
   Given a type T, its associated value type V is determined as follows:
     * If T is const-qualified, V is the associated value type of const-unqualified T.
     * Otherwise, if T is an array type, V is the cv-unqualified array element type.
     * Otherwise, a conditional value type C is determined first:
     * If T is a pointer type, C is the pointed-to type.
     * Otherwise, if T has nested types value_type and element_type:
     * If these types are the same (not considering cv-qualification), C is typename
       T::value_type.
     * Otherwise, C is undefined.
     * Otherwise, if T has the nested type value_type but not element_type, C is
       typename T::value_type.
     * Otherwise, if T has the nested type element_type but not value_type, C is
       typename T::element_type.
     * Otherwise, C is undefined.
   Then V is determined from C as follows:
     * If C is undefined, or C is not an object type, V is undefined.
     * Otherwise, V is cv-unqualified C.

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 retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
                       specializations (5,6) were ambiguous
   LWG 3446 C++20 for types having added specialization (8)
                       both value_type and element_type nested
                       types
                       LWG 3446 introduced hard error for
   LWG 3541 C++20 ambiguous cases added specialization (7)
                       that value_type and element_type are
                       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)

Category:
     * Todo no example