std::swap(std::function)

 

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std::function

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function::function

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function::operator=

function::swap

function::assign (until C++17)

function::operator bool

function::operator()

function::target_type

function::target

Non-member functions

operator==operator!= (until C++20)

swap(std::function)

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uses_allocator<std::function> (until C++17)

Deduction guides(C++17)

 

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)	specializes the std::swap algorithm (function)