Defined in header <functional>
template< class R, class... Args >
void swap( std::function<R(Args...)> &lhs, std::function<R(Args...)> &rhs ) noexcept;
(since C++11)

Overloads the std::swap algorithm for std::function. Exchanges the state of lhs with that of rhs. Effectively calls lhs.swap(rhs).


lhs, rhs - polymorphic function wrappers whose states to swap

Return value



#include <functional>
#include <iostream>
void foo(const char* str, int x) {
    std::cout << "foo(\"" << str << "\", " << x << ")\n";
void bar(const char* str, int x) {
    std::cout << "bar(\"" << str << "\", " << x << ")\n";
int main()
    std::function<void(const char*, int)> f1{ foo };
    std::function<void(const char*, int)> f2{ bar };
    f1("f1", 1);
    f2("f2", 2);
    std::cout << "std::swap(f1, f2);\n";
    std::swap(f1, f2);
    f1("f1", 1);
    f2("f2", 2);


foo("f1", 1)
bar("f2", 2)
std::swap(f1, f2);
bar("f1", 1)
foo("f2", 2)

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2062 C++11 overload of swap for function was not required to be noexcept required

See also

swaps the contents
(public member function)
overloads the std::swap algorithm

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