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 function called.
• Otherwise, exchanges values of rhs and * this . If an exception is thrown, the state of * this and rhs depends on exception safety of variant's move constructor.

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.