std::variant<Types...>::swap
void swap( variant& rhs ) noexcept(/* see below */); |
(1) | (since C++17) |
Swaps two variant
objects.
- if both
*this
andrhs
are valueless by exception, does nothing - otherwise, if both
*this
andrhs
hold the same alternative, calls swap(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>) && ...))
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