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std::variant::swap(3) | C++ Standard Libary | std::variant::swap(3) |
NAME¶
std::variant::swap - std::variant::swap
Synopsis¶
void swap( variant& rhs ) noexcept(/* see below */);
(since C++17)
(until C++20)
constexpr void swap( variant& rhs ) noexcept(/* see below */); (since
C++20)
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
Defect reports
The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.
DR Applied to Behavior as published Correct behavior
P2231R1 C++20 swap was not constexpr while the required made constexpr
operations can be constexpr in C++20
2022.07.31 | http://cppreference.com |