std::optional<T>::reset
From cppreference.com
void reset() noexcept; |
(since C++17) (constexpr 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.
Contents |
[edit] Notes
Feature-test macro | Value | Std | Feature |
---|---|---|---|
__cpp_lib_optional |
202106L | (C++20) (DR20) |
Fully constexpr |
[edit] Example
Run this code
#include <iostream> #include <optional> struct A { std::string s; A(std::string str) : s(std::move(str)) { std::cout << " constructed\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
[edit] Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
P2231R1 | C++20 | reset was not constexpr while non-trivial destruction is allowed in constexpr in C++20
|
made constexpr |
[edit] See also
assigns contents (public member function) |