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 member 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 member type
value_type (e.g., std::reverse_iterator). If T::value_type is an object 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 member type
element_type (e.g., std::shared_ptr). If T::element_type is an object type, provides
a member type value_type equal to std::remove_cv_t<typename T::element_type>.
Otherwise, there is no member value_type.
7-8) Specialization for types that define public and accessible member 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 retroactively to
previously published C++ standards.

DR Applied to Behavior as published Correct behavior
specializations were ambiguous for
LWG 3446 C++20 types containing a disambiguating
both value_type and element_type specialization added
member types
LWG 3446 introduced hard error for
LWG 3541 C++20 ambiguous cases that made resulting 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)