std::tuple<Types...>::swap

< cpp‎ | utility‎ | tuple

Defined in header `<tuple>`
	(1)
void swap( tuple& other ) noexcept(/* see below */);			(since C++11) (until C++20)
constexpr void swap( tuple& other ) noexcept(/* see below */);			(since C++20)
constexpr void swap( const tuple& other ) noexcept(/* see below */) const;		(2)	(since C++23)

Calls swap (which might be std::swap, or might be found via ADL) for each element in *this and its corresponding element in other.

If any selected `swap` function call is ill-formed, or does not swap the corresponding elements of both tuples, the behavior is undefined.	(until C++23)
If any selected `swap` function call does not swap the corresponding elements of both tuples, the behavior is undefined. 1) The program is ill-formed if (std::is_swappable_v<Types> && ...) is not true. 2) The program is ill-formed if (std::is_swappable_v<const Types> && ...) is not true.	(since C++23)

Parameters

other

tuple of values to swap

Return value

(none)

Exceptions

`noexcept` specification: noexcept( noexcept(swap(std::declval<T0&>>(), std::declval<T0&>())) && noexcept(swap(std::declval<T1&>>(), std::declval<T1&>())) && noexcept(swap(std::declval<T2&>>(), std::declval<T2&>())) && ... ) In the expression above, the identifier `swap` is looked up in the same manner as the one used by the C++17 std::is_nothrow_swappable trait.	(until C++17)
1) `noexcept` specification: noexcept((std::is_nothrow_swappable_v<Types> && ...)) 2) `noexcept` specification: noexcept((std::is_nothrow_swappable_v<const Types> && ...))	(since C++17)

Example

#include <iostream>
#include <string>
#include <tuple>
 
int main()
{
    std::tuple<int, std::string, float>
                      p1{42, "ABCD", 2.71},
                      p2;
    p2 = std::make_tuple(10, "1234", 3.14);
 
    auto print_p1_p2 = [&](auto rem) {
        std::cout << rem
                  << "p1 = {" << std::get<0>(p1)
                  << ", "     << std::get<1>(p1)
                  << ", "     << std::get<2>(p1) << "}, "
                  << "p2 = {" << std::get<0>(p2)
                  << ", "     << std::get<1>(p2)
                  << ", "     << std::get<2>(p2) << "}\n";
    };
 
    print_p1_p2("Before p1.swap(p2): ");
    p1.swap(p2);
    print_p1_p2("After  p1.swap(p2): ");
    swap(p1, p2);
    print_p1_p2("After swap(p1, p2): ");
}

Output:

Before p1.swap(p2): p1 = {42, ABCD, 2.71}, p2 = {10, 1234, 3.14}
After  p1.swap(p2): p1 = {10, 1234, 3.14}, p2 = {42, ABCD, 2.71}
After swap(p1, p2): p1 = {42, ABCD, 2.71}, p2 = {10, 1234, 3.14}

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR	Applied to	Behavior as published	Correct behavior
LWG 2456	C++11	the `noexcept` specification is ill-formed	made to work