std::copyable_function

Defined in header <functional> 
template< class... >
class copyable_function; // not defined
 (1) (since C++26) 
template< class R, class... Args >
class copyable_function<R(Args...)>;
template< class R, class... Args >
class copyable_function<R(Args...) noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) &>;
template< class R, class... Args >
class copyable_function<R(Args...) & noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) &&>;
template< class R, class... Args >
class copyable_function<R(Args...) && noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) const>;
template< class R, class... Args >
class copyable_function<R(Args...) const noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) const &>;
template< class R, class... Args >
class copyable_function<R(Args...) const & noexcept>;
template< class R, class... Args >
class copyable_function<R(Args...) const &&>;
template< class R, class... Args >
class copyable_function<R(Args...) const && noexcept>;
 (2) (since C++26)

Class template std::copyable_function is a general-purpose polymorphic function wrapper. std::copyable_function objects can store and invoke any CopyConstructible Callable target — functions, lambda expressions, bind expressions, or other function objects, as well as pointers to member functions and pointers to member objects.

The stored callable object is called the target of std::copyable_function. If a std::copyable_function contains no target, it is called empty. Unlike std::function, invoking an empty std::copyable_function results in undefined behavior.

std::copyable_functions supports every possible combination of cv-qualifiers, ref-qualifiers, and noexcept-specifiers not including volatile provided in its template parameter. These qualifiers and specifier (if any) are added to its operator().

std::copyable_function satisfies the requirements of CopyConstructible and CopyAssignable.

Member types

Type Definition
result_type R

Member functions

(C++26)
 constructs a new std::copyable_function object
(public member function)
(C++26)
 destroys a std::copyable_function object
(public member function)
(C++26)
 replaces or destroys the target
(public member function)
(C++26)
 swaps the targets of two std::copyable_function objects
(public member function)
(C++26)
 checks if the std::copyable_function has a target
(public member function)
(C++26)
 invokes the target
(public member function)

Non-member functions

(C++26)
 overloads the std::swap algorithm
(function)
(C++26)
 compares a std::copyable_function with nullptr
(function)

Notes

Implementations may store a callable object of small size within the std::copyable_function object. Such small object optimization is effectively required for function pointers and std::reference_wrapper specializations, and can only be applied to types T for which std::is_nothrow_move_constructible_v<T> is true.

Feature-test macro Value Std Feature
__cpp_lib_copyable_function 202306L (C++26) std::copyable_function

Example

See also

(C++11)
 wraps callable object of any copy constructible type with specified function call signature
(class template)
(C++23)
 wraps callable object of any type with specified function call signature
(class template)

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