NAME¶

std::copyable_function - std::copyable_function

Synopsis¶

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

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¶

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

Non-member functions¶

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

This section is incomplete
Reason: example

See also¶

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

Category:¶

* Todo with reason