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>
 
using Ex = std::expected<std::string, int>;
 
void show(const Ex& ex1, const Ex& ex2)
{
    for (int i{}; i < 2; ++i)
    {
        std::cout << (i ? "ex2" : "ex1");
        if (const Ex& ex = (i ? ex2 : ex1); ex.has_value())
            std::cout << ".has_value() = " << *ex << '\n';
        else
            std::cout << ".error() = " << ex.error() << '\n';
    }
}
 
int main()
{
    Ex ex1("\N{DOG FACE}");
    Ex ex2{"\N{BONE}"};
    show(ex1, ex2);
    swap(ex1, ex2);
    std::cout << "swap(ex1, ex2);\n";
    show(ex1, ex2);
    std::cout << '\n';
 
    ex2 = std::unexpected(13);
    show(ex1, ex2);
    swap(ex1, ex2);
    std::cout << "swap(ex1, ex2);\n";
    show(ex1, ex2);
    std::cout << '\n';
 
    ex2 = std::unexpected(19937);
    show(ex1, ex2);
    swap(ex1, ex2);
    std::cout << "swap(ex1, ex2);\n";
    show(ex1, ex2);
    std::cout << '\n';
}

ex1.has_value() = 🐶
ex2.has_value() = 🦴
swap(ex1, ex2);
ex1.has_value() = 🦴
ex2.has_value() = 🐶
 
ex1.has_value() = 🦴
ex2.error() = 13
swap(ex1, ex2);
ex1.error() = 13
ex2.has_value() = 🦴
 
ex1.error() = 13
ex2.error() = 19937
swap(ex1, ex2);
ex1.error() = 19937
ex2.error() = 13

See also