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) |
