std::swap(std::function)

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std::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

 swaps the contents
(public member function)
(C++23)
 specializes the std::swap algorithm
(function)
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