20 General utilities library [utilities]

20.6 Optional objects [optional]

20.6.3 Class template optional [optional.optional]

20.6.3.7 Modifiers [optional.mod]

constexpr void reset() noexcept;
Effects: If *this contains a value, calls val->T​::​~T() to destroy the contained value; otherwise no effect.
Postconditions: *this does not contain a value.