The following macro BSLSTL_OPTIONAL_USES_STD_ALIASES controls whether platform standard library is used as a basis for bsl types in the following ways: - bsl::nullopt is an alias to std::nullopt
Declared in <bslstl_optional.h>
#define BSLSTL_OPTIONAL_USES_STD_ALIASES
bsl::optional<T> inherits from std::optional<T> when T is not allocator-aware.
This macro does not control whether there are conversions and comparisons between std::optional and bsl::optional, that is conditioned only on whether std::optional is available (i.e., BSLS_LIBRARYFEATURES_HAS_CPP17_BASELINE_LIBRARY is defined).