View source for cpp/utility/functional/function ref

{{cpp/title|function_ref}}
{{cpp/utility/functional/function_ref/navbar}}
{{dcl begin}}
{{dcl header|functional}}
{{dcl|num=1|since=c++26|
template< class... >
class function_ref; // not defined
}}
{{dcl|num=2|since=c++26|
template< class R, class... Args >
class function_ref<R(Args...)>;
template< class R, class... Args >
class function_ref<R(Args...) noexcept>;
template< class R, class... Args >
class function_ref<R(Args...) const>;
template< class R, class... Args >
class function_ref<R(Args...) const noexcept>;
}}
{{dcl end}}

Class template {{tt|std::function_ref}} is a non-owning function wrapper. {{tt|std::function_ref}} objects can store and invoke reference to {{named req|Callable}} ''target'' - functions, [[cpp/language/lambda|lambda expressions]], [[cpp/utility/functional/bind|bind expressions]], or other function objects, but not pointers to member functions and pointers to member objects. {{c/core|std::nontype}} can be used to construct {{tt|std::function_ref}} by passing function pointers, pointers to member functions, and pointers to member objects.

{{tt|std::function_ref}}s supports every possible combination of [[cpp/language/member functions#const- and volatile-qualified member functions|cv-qualifiers]], and [[cpp/language/noexcept spec|noexcept-specifiers]] not including {{c/core|volatile}} provided in its template parameter.

Every specialization of {{tt|std::function_ref}} is a {{named req|TriviallyCopyable}} type that satisfies {{lconcept|copyable}}.

===Member objects===
{{dsc begin}}
{{dsc hitem|Member|Definition}}
{{dsc expos mem obj|bound-entity|an object that has an unspecified {{named req|TriviallyCopyable}} type {{tt|BoundEntityType}}, that satisfies {{lconcept|copyable}} and is capable of storing a pointer to object value or pointer to function value}}
{{dsc expos mem obj|thunk-ptr|a pointer to function of type {{c|R(*)(BoundEntityType, Args&&...) noexcept(/*noex*/)}} where {{c|/*noex*/}} is {{c/core|true}} if {{c/core|noexcept}} is present in function signature as part of the template parameter of {{tt|std::function_ref}}}}
{{dsc end}}

===Member functions===
{{dsc begin}}
{{dsc inc|cpp/utility/functional/function_ref/dsc constructor}}
{{dsc inc|cpp/utility/functional/function_ref/dsc operator{{=}}}}
{{dsc inc|cpp/utility/functional/function_ref/dsc operator()}}
{{dsc end}}

==={{rl|deduction guides|Deduction guides}}===

===Notes===
{{feature test macro|__cpp_lib_function_ref|std=C++26|value=202306L|{{tt|std::function_ref}}}}

===Example===
{{todo|example}}

===See also===
{{dsc begin}}
{{dsc inc|cpp/utility/functional/dsc function}}
{{dsc inc|cpp/utility/functional/dsc copyable_function}}
{{dsc inc|cpp/utility/functional/dsc move_only_function}}
{{dsc inc|cpp/utility/dsc nontype}}
{{dsc end}}

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