bsl::optional::optional

If the optional base class of the specified original holds a value, create an optional object whose contained value is initialized by moving from that value; otherwise, create a disengaged optional object. Use the specified allocator to supply memory. original is left in a valid, but unspecified state. Note that this constructor does not participate in overload resolution unless optional is an accessible base class of t_DERIVED or t_DERIVED is optional itself (in which case the instantiation provides the allocator‐extended move constructor).