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std::optional::reset(3) C++ Standard Libary std::optional::reset(3) NAME std::optional::reset - std::optional::reset Synopsis void reset() noexcept; (since C++17) (until C++20) constexpr void reset() noexcept; (since C++20) If *this contains a value, destroy that value as if by value().T::~T(). Otherwise, there are no effects. *this does not contain a value after this call. Example // Run this code #include <optional> #include <iostream> struct A { std::string s; A(std::string str) : s(std::move(str)) { std::cout << " con- structed\n"; } ~A() { std::cout << " destructed\n"; } A(const A& o) : s(o.s) { std::cout << " copy constructed\n"; } A(A&& o) : s(std::move(o.s)) { std::cout << " move constructed\n"; } A& operator=(const A& other) { s = other.s; std::cout << " copy assigned\n"; return *this; } A& operator=(A&& other) { s = std::move(other.s); std::cout << " move assigned\n"; return *this; } }; int main() { std::cout << "Create empty optional:\n"; std::optional<A> opt; std::cout << "Construct and assign value:\n"; opt = A("Lorem ipsum dolor sit amet, consectetur adipiscing elit nec."); std::cout << "Reset optional:\n"; opt.reset(); std::cout << "End example\n"; } Output: Create empty optional: Construct and assign value: constructed move constructed destructed Reset optional: destructed End example Defect reports The following behavior-changing defect reports were applied retroac- tively to previously published C++ standards. DR Applied to Behavior as published Correct behavior P2231R1 C++20 reset was not constexpr while non-trivial made constexpr destruction is allowed in constexpr in C++20 See also operator= assigns contents (public member function) http://cppreference.com 2022.07.31 std::optional::reset(3)
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