Support build environment where `<format>` is not available

[mingxwa]

In our company, std::format is not available in our production environment even though we use C++20. I was thinking about using the proxy library to replace virtual functions to improve the performance of our program.

Originally posted by @zhiyongww in #287 (comment)

[mingxwa]

Hi @zhiyongww, thank you for the insights. Let's defer the discussion to this issue. Could you help review #289 and let me know if it works for your scenario?

[zhiyongww]

Hi @mingxwa, thanks for the PR, it works for me right now. However, there was a minor issue that I was able to fix on my end by deleting:

proxy/proxy.h

Lines 45 to 47 in 7e80cef

	#if __cpp_static_call_operator >= 202207L
	#define ___PRO_STATIC_CALL(__R, ...) static __R operator()(__VA_ARGS__)
	#else

The error message:

fbcode/scripts/zhiyongww/proxy.h:515:3: error: declaring overloaded 'operator()' as 'static' is a C++23 extension [-Werror,-Wc++23-extensions]
  515 |   ___PRO_STATIC_CALL(void, T&& self, proxy<F>& rhs)
      |   ^
fbcode/scripts/zhiyongww/proxy.h:48:49: note: expanded from macro '___PRO_STATIC_CALL'
   48 | #define ___PRO_STATIC_CALL(__R, ...) static __R operator()(__VA_ARGS__)

[mingxwa]

@zhiyongww This is a known issue in Clang when building with the C++20 standard. If your project is not ready for upgrading to C++23, you can specify "-Wno-c++23-extensions" (this won't work for Clang 16) or "-Wno-c++2b-extensions" (see how we use it in our unit tests).

[zhiyongww]

Thanks, "-Wno-c++2b-extensions" works for me.