std::function_ref

Defined in header <functional>

Defined in header `<functional>`
template< class... > class function_ref; // not defined	(1)	(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>;	(2)	(since C++26)

template< class... >
class function_ref; // not defined

(1)

(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>;

(2)

(since C++26)

Class template std::function_ref is a non-owning function wrapper. std::function_ref objects can store and invoke reference to Callable target - functions, lambda expressions, bind expressions, or other function objects, but not pointers to member functions and pointers to member objects. std::nontype can be used to construct std::function_ref by passing function pointers, pointers to member functions, and pointers to member objects.

std::function_refs supports every possible combination of cv-qualifiers (excluding volatile), and noexcept-specifiers provided in its template parameter.

Every specialization of std::function_ref is a TriviallyCopyable type that satisfies copyable.

Member types

Member	Definition
`BoundEntityType` (private)	unspecified TriviallyCopyable type that satisfies `copyable` and is capable of storing a pointer to object value or pointer to function value (exposition-only member type*)
`FunctionPointerType` (private)	R()(`BoundEntityType` ,Args&&...)noexcept(noex ) where noex is `true` if noexcept is present in function signature as part of the template parameter of `std::function_ref`, `false` otherwise (exposition-only member type)

Data members

Member	Definition
`BoundEntityType` `bound-entity`	a bound entity object (exposition-only member object*)
`FunctionPointerType` `thunk-ptr`	a stored pointer to function (exposition-only member object*)

Member functions

(constructor)	constructs a new `function_ref` object (public member function)
operator=	assigns a `function_ref` (public member function)
operator()	invokes the stored thunk of a `function_ref` (public member function)

Deduction guides

Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_function_ref`	`202306L`	(C++26)	`std::function_ref`

Example

function (C++11)	copyable wrapper of any copy constructible callable object (class template)
copyable_function (C++26)	copyable wrapper of any copy constructible callable object that supports qualifiers in a given call signature (class template)
move_only_function (C++23)	move-only wrapper of any callable object that supports qualifiers in a given call signature (class template)
nontype nontype_t (C++26)	value construction tag (tag)

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