BSLSTL_OPTIONAL_CONSTEXPR17 controls whether constructors that are constexpr in C++17 std::optional are constexpr in bsl::optional for allocator-unaware types.
BSLSTL_OPTIONAL_CONSTEXPR17
constexpr
std::optional
bsl::optional
Declared in <bslstl_optional.h>
<bslstl_optional.h>
#define BSLSTL_OPTIONAL_CONSTEXPR17