use target_compile_definitions for REFLECTCPP_USE_STD_EXPECTED instea…

[BestITUserEUW]

…d of CMAKE_CXX_FLAGS. Addresses #506

[gemini-code-assist]

Summary of Changes

Hello @BestITUserEUW, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request updates the CMake build system to improve how the REFLECTCPP_USE_STD_EXPECTED preprocessor definition is handled. It transitions from using the global CMAKE_CXX_FLAGS to the more precise target_compile_definitions command. This change enhances the modularity and robustness of the build configuration by ensuring that the definition is applied only to the relevant target, addressing issue #506.

Highlights

• CMake Refactoring: The build configuration has been refactored to use a more modern and robust approach for defining preprocessor macros.
• Improved Macro Definition: The REFLECTCPP_USE_STD_EXPECTED preprocessor definition is now applied using target_compile_definitions instead of directly modifying CMAKE_CXX_FLAGS.
• Targeted Definitions: This change ensures that the definition is applied specifically to the reflectcpp target, preventing potential global side effects and improving build system clarity.

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[gemini-code-assist]

Code Review

The pull request correctly replaces the direct modification of CMAKE_CXX_FLAGS with target_compile_definitions, which is a good practice in modern CMake. My review includes a suggestion to further refactor the CMake logic to improve maintainability and robustness by consolidating conditional checks and using target-specific properties for C++ standard requirements.

[gemini-code-assist]

This change correctly uses target_compile_definitions, which is an improvement. However, it introduces a second if(REFLECTCPP_USE_STD_EXPECTED) block, duplicating the check from line 28. This can make the build logic harder to follow and maintain.

To consolidate this logic and make the CMake script more robust and modern, I'd suggest using target_compile_features to specify C++ standard requirements directly on the reflectcpp target. This would also provide better error messages if an incompatible C++ standard is used.

You could replace this new block and the one at lines 28-38 with a single block after add_library(reflectcpp ...):

# After add_library(reflectcpp ...)
if(REFLECTCPP_USE_STD_EXPECTED)
    target_compile_features(reflectcpp PUBLIC cxx_std_23)
    target_compile_definitions(reflectcpp PUBLIC REFLECTCPP_USE_STD_EXPECTED)
else()
    target_compile_features(reflectcpp PUBLIC cxx_std_20)
endif()

This would remove the need to manipulate the global CMAKE_CXX_STANDARD variable and centralize the feature configuration for the reflectcpp target.

[liuzicheng1987]

@BestITUserEUW thanks!