std::swap(std::variant)

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std::variant

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Observers
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Defined in header`<variant>`
template<class...Types> void swap(std::variant<Types...>& lhs, std::variant<Types...>& rhs)noexcept(/* see below */);		(since C++17) (constexpr since C++20)

Overloads thestd::swap algorithm forstd::variant. Effectively callslhs.swap(rhs).

This overload participates in overload resolution only ifstd::is_move_constructible_v<T_i> andstd::is_swappable_v<T_i> are bothtrue for allT_i inTypes....

[edit]Parameters

lhs, rhs - variant objects whose values to swap

[edit]Return value

(none)

[edit]Exceptions

noexcept specification:

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

[edit]Notes

Feature-test macro	Value	Std	Feature
`__cpp_lib_variant`	`202106L`	(C++20) (DR)	Fullyconstexpr`std::variant`

[edit]Example

Run this code

#include <iostream>#include <string>#include <variant> void print(autoconst& v,char term='\n'){std::visit([](auto&& o){std::cout<< o;}, v);std::cout<< term;} int main(){std::variant<int,std::string> v1{123}, v2{"XYZ"};    print(v1,' ');    print(v2); std::swap(v1, v2);    print(v1,' ');    print(v2); std::variant<double,std::string> v3{3.14};// std::swap(v1, v3); // ERROR: ~ inconsistent parameter packs}