# std::swap(std::function)

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< cpp‎ | utility‎ | functional‎ | function

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).

### Parameters

lhs, rhs | - | polymorphic function wrappers whose states to swap

### Return value

(none)

### Example

Run this code

    #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);
    }

Output:

    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

swap | swaps the contents (public member function)
swap(std::move_only_function) (C++23) | overloads the std::swap algorithm (function)

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