std::optional<T>::swap

Swaps the contents with those of other.

# Declarations

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

(since C++17) (constexpr since C++20)

# Parameters

other: the optional object to exchange the contents with

# Return value

(none)

# Example

#include <iostream>
#include <optional>
#include <string>
 
int main()
{
    std::optional<std::string> opt1("First example text");
    std::optional<std::string> opt2("2nd text");
 
    enum Swap { Before, After };
    auto print_opts = [&](Swap e)
    {
        std::cout << (e == Before ? "Before swap:\n" : "After swap:\n");
        std::cout << "opt1 contains '" << opt1.value_or("") << "'\n";
        std::cout << "opt2 contains '" << opt2.value_or("") << "'\n";
        std::cout << (e == Before ? "---SWAP---\n": "\n");
    };
 
    print_opts(Before);
    opt1.swap(opt2);
    print_opts(After);
 
    // Swap with only 1 set
    opt1 = "Lorem ipsum dolor sit amet, consectetur tincidunt.";
    opt2.reset();
 
    print_opts(Before);
    opt1.swap(opt2);
    print_opts(After);
}

# Defect reports

DR	Applied to	Behavior as published	Correct behavior
P2231R1	C++20	swap was not constexpr while the required operations can be constexpr in C++20	made constexpr

std::optional<T>::swap

# Declarations

# Parameters

# Return value

# Example

# Defect reports

# See also