std::swap(std::variant) - cppreference.com (original) (raw)

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

Overloads the std::swap algorithm for std::variant. Effectively calls lhs.swap(rhs).

This overload participates in overload resolution only if std::is_move_constructible_v<T_i> and std::is_swappable_v<T_i> are both true for all T_i in Types....

Contents

• 1 Parameters
• 2 Return value
• 3 Exceptions
• 4 Notes
• 5 Example
• 6 Defect reports
• 7 See also

[edit] Parameters

[edit] Return value

(none)

[edit] Exceptions

noexcept

specification:

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

[edit] Notes

[edit] Example

#include #include #include   void print(auto const& 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 }

Output:

[edit] Defect reports

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

[edit] See also

| | swaps with another variant (public member function) [edit] | | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |