# swap(std::move_only_function)

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< cpp‎ | utility‎ | functional‎ | move only function

friend void swap( move_only_function& lhs, move_only_function& rhs ) noexcept; |  | (since C++23)

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

This function is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when `std::move_only_function<FunctionType>` is an associated class of the arguments.

### Parameters

lhs, rhs | - | `std::move_only_function` objects whose states to swap

### Return value

(none)

### Example

Run this code

    #include <concepts>
    #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::move_only_function<void(const char*, int) const> f1{ foo };
        std::move_only_function<void(const char*, int) const> f2{ bar };

        f1("f1", 1);
        f2("f2", 2);

        std::cout << "std::ranges::swap(f1, f2);\n";
        std::ranges::swap(f1, f2); // finds the hidden friend

        f1("f1", 1);
        f2("f2", 2);
    }

Output:

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

### See also

swap (C++23) | swaps the targets of two `std::move_only_function` objects (public member function)
std::swap(std::function) (C++11) | specializes the std::swap algorithm (function template)

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