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std::function<R(Args...)>::swap - cppreference.com

From cppreference.com

void swap( function& other ) noexcept;

 (since C++11)

Exchanges the stored callable objects of *this and other.

Parameters

other - function wrapper to exchange the stored callable object with

Return value

(none)

Example

#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 << "f1.swap(f2);\n";
    f1.swap(f2);

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

Output: 

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

See also

swaps the targets of two std::move_only_function objects
(public member function of std::move_only_function) [edit]