swap(std::expected)

 

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std::expected

Member functions

expected::expected

expected::~expected

expected::operator=

Observers

expected::operator->expected::operator*

expected::operator boolexpected::has_value

expected::value

expected::error

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Monadic operations

expected::and_then

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expected::transform_error

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expected::emplace

expected::swap

Non-member functions

operator==(std::expected)

swap(std::expected)

Helper classes

unexpected

bad_expected_access

unexpect_tunexpect

 

friendconstexprvoid swap( expected& lhs, expected& rhs )noexcept(/*see below*/);		(since C++23)

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

lhs, rhs

-

expected objects whose states to swap

Return value

(none)

Exceptions

noexcept specification:  

noexcept(noexcept(lhs.swap(rhs)))

Example

Run this code

#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';elsestd::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';}

Output:

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

swap	exchanges the contents (public member function)