std::basic_common_reference<std::reference_wrapper>

 

C++

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Feature test macros (C++20)

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Concepts library (C++20)

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Ranges library (C++20)

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Symbols index

External libraries

 

Utilities library

Language support Type support (basic types, RTTI) Library feature-test macros (C++20) Dynamic memory management Program utilities Coroutine support (C++20) Variadic functions is_constant_evaluated (C++20) is_within_lifetime (C++26) initializer_list (C++11) source_location (C++20) Three-way comparison three_way_comparablethree_way_comparable_with (C++20)(C++20) strong_ordering (C++20) weak_ordering (C++20) partial_ordering (C++20) common_comparison_category (C++20) compare_three_way_result (C++20) compare_three_way (C++20) strong_order (C++20) weak_order (C++20) partial_order (C++20) compare_strong_order_fallback (C++20) compare_weak_order_fallback (C++20) compare_partial_order_fallback (C++20)   is_eqis_ltis_lteq (C++20)(C++20)(C++20)   is_neqis_gtis_gteq (C++20)(C++20)(C++20)

General utilities Date and time Function objects Formatting library (C++20)   bitset hash (C++11) Relational operators (deprecated in C++20) rel_ops::operator!=rel_ops::operator>    rel_ops::operator<=rel_ops::operator>= Integer comparison functions cmp_equalcmp_lesscmp_less_than (C++20)(C++20)(C++20)   cmp_not_equalcmp_greatercmp_greater_than (C++20)(C++20)(C++20) in_range (C++20) Swap and type operations swap ranges::swap (C++20) exchange (C++14) declval (C++11) to_underlying (C++23) forward (C++11) forward_like (C++23) move (C++11) move_if_noexcept (C++11) as_const (C++17) Common vocabulary types pair tuple (C++11) optional (C++17) any (C++17) variant (C++17) tuple_size (C++11) tuple_element (C++11) apply (C++17) make_from_tuple (C++17) expected (C++23) Elementary string conversions to_chars (C++17) from_chars (C++17) chars_format (C++17) to_chars_result (C++17) from_chars_result (C++17)

 

Function objects

Function wrappers function (C++11) move_only_function (C++23) copyable_function (C++26) function_ref (C++26) mem_fn (C++11) bad_function_call (C++11)	Partial function application bind_frontbind_back (C++20)(C++23) bind (C++11) is_bind_expression (C++11) is_placeholder (C++11) _1, _2, _3, ... (C++11)
Function invocation invokeinvoke_r (C++17)(C++23) Identity function object identity (C++20)	Reference wrappers reference_wrapper (C++11) refcref (C++11)(C++11) unwrap_referenceunwrap_ref_decay (C++20)(C++20)
Operator wrappers plus minus negate multiplies divides modulus bit_and bit_or bit_not (C++14)   bit_xor equal_to not_equal_to greater less greater_equal less_equal logical_and logical_or logical_not	Transparent operator wrappers plus<> (C++14) minus<> (C++14) negate<> (C++14) multiplies<> (C++14)   divides<> (C++14) modulus<> (C++14) bit_and<> (C++14) bit_or<> (C++14) bit_not<> (C++14) bit_xor<> (C++14) equal_to<> (C++14) not_equal_to<> (C++14) greater<> (C++14) less<> (C++14) greater_equal<> (C++14) less_equal<> (C++14) logical_and<> (C++14) logical_or<> (C++14) logical_not<> (C++14)
Negators not_fn (C++17) Searchers default_searcher (C++17) boyer_moore_searcher (C++17) boyer_moore_horspool_searcher (C++17)	Constrained comparators ranges::equal_to (C++20) ranges::not_equal_to (C++20) ranges::greater (C++20) ranges::less (C++20) ranges::greater_equal (C++20) ranges::less_equal (C++20) compare_three_way (C++20)
Old binders and adaptors
unary_function (until C++17*) binary_function (until C++17*) ptr_fun (until C++17*) pointer_to_unary_function (until C++17*) pointer_to_binary_function (until C++17*)   mem_fun (until C++17*) mem_fun_tmem_fun1_tconst_mem_fun_tconst_mem_fun1_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) not1 (until C++20*) not2 (until C++20*)	binder1stbinder2nd (until C++17*)(until C++17*) bind1stbind2nd (until C++17*)(until C++17*) mem_fun_ref (until C++17*) mem_fun_ref_tmem_fun1_ref_tconst_mem_fun_ref_tconst_mem_fun1_ref_t (until C++17*)(until C++17*)(until C++17*)(until C++17*) unary_negate (until C++20*) binary_negate (until C++20*)

 

std::reference_wrapper

Member functions

reference_wrapper::reference_wrapper

reference_wrapper::operator=

reference_wrapper::getreference_wrapper::operator T&

reference_wrapper::operator()

Non-member functions

operator==operator<=> (C++26)(C++26)

Deduction guides (C++17)

Helper classes

basic_common_reference<std::reference_wrapper> (C++23)

 

Defined in header <functional>
template< class R, class T,           template<class> RQual, template<class> TQual >     requires (/*ref-wrap-common-reference-exists-with*/<R, T, RQual<R>, TQual<T>> &&               !/*ref-wrap-common-reference-exists-with*/<T, R, TQual<T>, RQual<R>>) struct basic_common_reference<R, T, RQual, TQual>;	(1)	(since C++23)
template< class T, class R,           template<class> TQual, template<class> RQual >     requires (/*ref-wrap-common-reference-exists-with*/<R, T, RQual<R>, TQual<T>> &&               !/*ref-wrap-common-reference-exists-with*/<T, R, TQual<T>, RQual<R>>) struct basic_common_reference<T, R, TQual, RQual>;	(2)	(since C++23)
Helper concepts
template< class R, class T, class RQ, class TQ > concept /*ref-wrap-common-reference-exists-with*/ =     /*is-ref-wrapper*/<R> &&     requires { typename std::common_reference_t<typename R::type&, TQ>; } &&     std::convertible<RQ, std::common_reference_t<typename R::type&, TQ>>;	(3)	(exposition only*)

The common reference type of a reference_wrapper (denoted as R) and a type T, correspondingly applied with cv and reference qualifiers (denoted as RQ and TQ respectively), is equivalent to a common reference type of underlying type of R applied with lvalue reference and the TQ.

The common reference type is defined only if R is the only reference_wrapper, the underlying type of R applied with lvalue reference and the TQ have a common reference type to which RQ must be convertible.

The exposition-only constant /*is-ref-wrapper*/<R> is true if and only if R is a specialization of std::reference_wrapper.

Member types

Member type	Definition
type	std::common_reference_t<typename R::type&, TQual<T>> (1,2)

Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_common_reference_wrapper	202302L	(C++23)	Make std::common_reference_t of std::reference_wrapper a reference type

Example

Run this code

#include <concepts>
#include <functional>
 
static_assert(std::same_as<std::common_reference_t<int&,
                                                   std::reference_wrapper<int>>,
                                                   int&>);
static_assert(std::same_as<std::common_reference_t<std::reference_wrapper<int>&,
                                                   int&>,
                                                   int&>);
static_assert(std::same_as<std::common_reference_t<int&,
                                                   const std::reference_wrapper<int>&>,
                                                   int&>);
int main() {}

See also

common_referencebasic_common_reference (C++20)

determines the common reference type of a group of types (class template)