If this object is non-null, return a copy of the underlying object of a (template parameter) t_TYPE created using the provided allocator, and the specified value converted to t_TYPE using the specified allocator otherwise. Note that this method returns by value, so may be inefficient in some contexts.
Declared in <bslstl_optional.h>
template<class t_ANY_TYPE>
t_TYPE
value_or(
std::allocator_arg_t,
allocator_type allocator,
t_ANY_TYPE&& value) &&;