swap (std::expected)

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

This overload participates in overload resolution only if lhs. swap ( rhs ) is valid.

This function is not visible to ordinary unqualified or qualified lookup , and can only be found by argument-dependent lookup when std:: expected < T, E > is an associated class of the arguments.

Parameters

Return value

(none)

Exceptions

Example

#include <expected>
#include <iostream>
#include <string_view>
using Ex = std::expected<std::string, int>;
void show(const Ex& ex1, const Ex& ex2, std::string_view term = "\n")
{
    for (int i{}; i != 2; ++i)
    {
        std::cout << (i ? "ex2" : "ex1");
        if (const Ex& ex = (i ? ex2 : ex1); ex.has_value())
            std::cout << ".value() = " << *ex << "  ";
        else
            std::cout << ".error() = " << ex.error() << "  ";
    }
    std::cout << term;
}
int main()
{
    Ex ex1("\N{SMILING FACE WITH SUNGLASSES}");
    Ex ex2{"\N{SLIGHTLY SMILING FACE}"};
    show(ex1, ex2, "after swap(ex1, ex2):\n");
    std::swap(ex1, ex2);
    show(ex1, ex2, "\n\n");
    ex2 = std::unexpected(13);
    show(ex1, ex2, "after swap(ex1, ex2):\n");
    std::swap(ex1, ex2);
    show(ex1, ex2, "\n\n");
    ex2 = std::unexpected(37);
    show(ex1, ex2, "after swap(ex1, ex2):\n");
    std::swap(ex1, ex2);
    show(ex1, ex2);
}

ex1.value() = 😎  ex2.value() = 🙂  after swap(ex1, ex2):
ex1.value() = 🙂  ex2.value() = 😎  
ex1.value() = 🙂  ex2.error() = 13  after swap(ex1, ex2):
ex1.error() = 13  ex2.value() = 🙂  
ex1.error() = 13  ex2.error() = 37  after swap(ex1, ex2):
ex1.error() = 37  ex2.error() = 13

See also