std::variant<Types...>::swap

Swaps two variant objects.

• If both *this and rhs are valueless by exception, does nothing.
• Otherwise, if both *this and rhs hold the same alternative, calls swap( * std::get_if <i> (this), * std::get_if <i> ( std::addressof (rhs) ) ) where i is index(). If an exception is thrown, the state of the values depends on the exception safety of the swap
• Otherwise, exchanges values of rhs and *this. If an exception is thrown, the state of *this and rhs

The program is ill-formed unless type T_i are Swappable and std::is_move_constructible_v<T_i> is true for all T_i in Types...

Parameters

Return value

(none)

Exceptions

If this- >index( ) == rhs.index ( ) , may throw any exception thrown by swap( * std::get_if <i> (this), * std::get_if <i> ( std::addressof (rhs) ) ) with i being index()

Otherwise, may throw any exception thrown by the move constructors of the alternatives currently held by *this and rhs

Notes

Example

#include <iostream>
#include <string>
#include <variant>
 
int main()
{
    std::variant<int, std::string> v1{2}, v2{"abc"};
    std::visit([](auto&& x) { std::cout << x << ' '; }, v1);
    std::visit([](auto&& x) { std::cout << x << '\n'; }, v2);
    v1.swap(v2);
    std::visit([](auto&& x) { std::cout << x << ' '; }, v1);
    std::visit([](auto&& x) { std::cout << x << '\n'; }, v2);
}

2 abc
abc 2

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

See also