std::pair<T1,T2>::swap

Since C++20

Swaps first with other.first and second with other.second, as if by using std::swap; swap(first, other.first); swap(second, other.second);.

# Declarations

void swap( pair& other ) noexcept(/* see below */);

(since C++11) (until C++20)

constexpr void swap( pair& other ) noexcept(/* see below */);

(since C++20)

constexpr void swap( const pair& other ) const noexcept(/* see below */);

(since C++23)

# Parameters

other: pair of values to swap

# Return value

(none)

# Example

#include <iostream>
#include <utility>
#include <string>
int main()
{
    std::pair<int, std::string> p1(10, "test"), p2;
    p2.swap(p1);
    std::cout << "(" << p2.first << ", " << p2.second << ")\n";
 
#if __cpp_lib_ranges_zip >= 202110L
    // Using the C++23 const qualified swap overload
    // (swap is no longer propagating pair constness)
    int i1 = 10, i2{};
    std::string s1("test"), s2;
    const std::pair<int&, std::string&> r1(i1, s1), r2(i2, s2);
    r2.swap(r1);
    std::cout << "(" << i2 << ", " << s2 << ")\n";
#endif
}

# Defect reports

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