Use of TOKEN_PASTE was a bad idea at the first place. Just use ## everywhere. Nobody practically lacks token pasting.
Oracle Developer Studio's C++ preprocessor started to understand __has_cpp_attribute since version 12.5, and is broken. After looking around for a while I found Boost and ICU also had this issue before. Let me add workaround for it.
To fix build failures.
Devs do not love "impl".