Compilation Error with REFLECTCPP_USE_STD_EXPECTED=ON

[danielmohansahu]

I'm seeing the following compilation error when building reflect-cpp v0.23.0 (commit c241a201fed6386acc7f1484ade4adaaaf75d2f8) using the REFLECTCPP_USE_STD_EXPECTED flag:

$ cmake -S . -B build -DREFLECTCPP_USE_STD_EXPECTED=ON -DCMAKE_CXX_STANDARD=23
-- The CXX compiler identification is GNU 13.3.0
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/bin/c++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Configuring done (0.2s)
-- Generating done (0.0s)
-- Build files have been written to: /home/daniel/Code/reflect-cpp/build
$ cmake --build build
[ 20%] Building CXX object CMakeFiles/reflectcpp.dir/cmake_pch.hxx.gch
In file included from /home/daniel/Code/reflect-cpp/include/rfl/Literal.hpp:13,
                 from /home/daniel/Code/reflect-cpp/include/rfl/Field.hpp:8,
                 from /home/daniel/Code/reflect-cpp/include/rfl/AddStructName.hpp:6,
                 from /home/daniel/Code/reflect-cpp/include/rfl.hpp:10,
                 from /home/daniel/Code/reflect-cpp/build/CMakeFiles/reflectcpp.dir/cmake_pch.hxx:5,
                 from <command-line>:
/home/daniel/Code/reflect-cpp/include/rfl/Result.hpp:457:14: error: expected identifier before ‘this’
  457 |   auto error(this Self&& self) noexcept {
      |              ^~~~
/home/daniel/Code/reflect-cpp/include/rfl/Result.hpp:457:14: error: expected ‘,’ or ‘...’ before ‘this’
/home/daniel/Code/reflect-cpp/include/rfl/Result.hpp: In member function ‘auto std::bad_expected_access<rfl::Error>::error(int)’:
/home/daniel/Code/reflect-cpp/include/rfl/Result.hpp:458:31: error: ‘self’ was not declared in this scope; did you mean ‘Self’?
  458 |     return std::forward<Self>(self).err_;
      |                               ^~~~
      |                               Self
gmake[2]: *** [CMakeFiles/reflectcpp.dir/build.make:80: CMakeFiles/reflectcpp.dir/cmake_pch.hxx.gch] Error 1
gmake[1]: *** [CMakeFiles/Makefile2:87: CMakeFiles/reflectcpp.dir/all] Error 2
gmake: *** [Makefile:156: all] Error 2

Setting -DREFLECTCPP_USE_STD_EXPECTED=OFF builds fine.

I'm using gcc 13.3.0 on Ubuntu 24.04 - happy to provide other environment information if helpful.

[liuzicheng1987]

@danielmohansahu , I can reproduce the problem.

[liuzicheng1987]

@danielmohansahu , I have checked - we indeed did not support using gcc 13 with std::expected. To be fair, if you want to fully make use of C++ 23 features, you should probably be using gcc 14 or above anyway.

However, I found out that with a few tweaks here and there you can get it to work, so I have done that, see #572