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

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< cpp‎ | utility‎ | variant

void swap( variant& rhs ) noexcept(/* see below */); | (1) | (since C++17)

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<i>(*this), std:get<i>(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 behavior is undefined unless lvalues of type `T_i` are Swappable and std::is_move_constructible_v <T_i> is `true` for all `T_i` in `Types...`.

### Parameters

rhs | - | a variant object to swap with

### Return value

(none)

### Exceptions

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

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

`noexcept` specification:
noexcept((( std::is_nothrow_move_constructible_v <Types> &&
std::is_nothrow_swappable_v <Types>) && ...))

### Example

Run this code

    #include <variant>
    #include <string>
    #include <iostream>

    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);
    }

Output:

    2 abc
    abc 2

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