Compiling with Android NDK fails to resolve gsl

[rockaport]

The Android NDK is kind of funky. While it does have std::span, its version header doesn't include the __cpp_lib_span feature test macro and compilation fails to resolve gsl in defining the template in uuid.h.

include/uuid.h:52:17: error: use of undeclared identifier 'gsl'

I think this is all that's needed to fix the issue in uuid.h

#ifndef __cpp_lib_span
#include <gsl/gsl>
#endif

It also looks like even though this cmake option is default OFF, the gsl header is never being included.
option(UUID_USING_CXX20_SPAN "Using span from std instead of gsl" OFF)

[mariusbancila]

I don't have an Android NDK. Have you tried your fix? If so, can you do a PR?

[masoud-al]

I can confirm that by defining __cpp_lib_span manually and using c++20 uuid.h compiles without any modification. I tested on NDK version 25.2.9519653.