std::variant<Types...>::swap
Declarations
C++17
void swap( variant& rhs ) noexcept(/* see below */);
C++20
constexpr void swap( variant& rhs ) noexcept(/* see below */);
Swaps two variant objects.
- If both
*this
andrhs
are valueless by exception, does nothing - Otherwise, if both
*this
andrhs
hold the same alternative, callsswap(std::get<i>(*this), std::get<i>(rhs))
wherei
isindex()
. 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
andrhs
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
#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);
}
2 abc
abc 2