std::optional<T>::reset

If *this contains a value, destroy that value as if by value().T::~T(). Otherwise, there are no effects.

# Declarations

void reset() noexcept;

(since C++17) (constexpr since C++20)

# Notes

Feature-test macro Value Std Feature __cpp_lib_optional 202106L (C++20)(DR20) Fully constexpr

# Example

#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";
}

# Defect reports

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

# See also

operator=