Create an optional object having the value of the (template parameter) t_TYPE created in place using the specified il and specified args. Use the currently installed default allocator to supply memory. This constructor can be called in constant expressions only when t_TYPE is not allocator-aware.
Declared in <bslstl_optional.h>
template<
class t_INIT_LIST_TYPE,
class... t_ARGS>
constexpr
explicit
optional(
std::in_place_t,
std::initializer_list<t_INIT_LIST_TYPE> il,
t_ARGS&&... args);