std:: swap (std::optional)

Overloads the std::swap algorithm for std::optional . Exchanges the state of lhs with that of rhs . Effectively calls lhs. swap ( rhs ) .

This overload participates in overload resolution only if std:: is_move_constructible_v < T > and std:: is_swappable_v < T > are both true .

Parameters

Return value

(none)

Exceptions

Notes

Example

#include <iostream>
#include <optional>
#include <string>
int main()
{
    std::optional<std::string> a{"██████"}, b{"▒▒▒▒▒▒"};
    auto print = [&](auto const& s)
    {
        std::cout << s << "\t"
                     "a = " << a.value_or("(null)") << "  "
                     "b = " << b.value_or("(null)") << '\n';
    };
    print("Initially:");
    std::swap(a, b);
    print("swap(a, b):");
    a.reset();
    print("\n""a.reset():");
    std::swap(a, b);
    print("swap(a, b):");
}

Initially:   a = ██████  b = ▒▒▒▒▒▒
swap(a, b):  a = ▒▒▒▒▒▒  b = ██████
a.reset():   a = (null)  b = ██████
swap(a, b):  a = ██████  b = (null)

Defect reports

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

See also