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

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

This overload participates in overload resolution only if std::is_move_constructible_v<T> and std::is_swappable_v<T> are both true.

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   int main() { std::optional<std::string> a{"██████"}, b{"▒▒▒▒▒▒"};   auto print = [&](auto const& s) { std::cout << s << "\t" "a = " << a.value_or("(null)") << " " "b = " << b.value_or("(null)") << '\n'; };   print("Initially:"); std::swap(a, b); print("swap(a, b):"); a.reset(); print("\n""a.reset():"); std::swap(a, b); print("swap(a, b):"); }

Output:

Initially: a = ██████ b = ▒▒▒▒▒▒ swap(a, b): a = ▒▒▒▒▒▒ b = ██████   a.reset(): a = (null) b = ██████ swap(a, b): a = ██████ b = (null)

[edit] Defect reports

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

[edit] See also

| | exchanges the contents (public member function) [edit] | | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |