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Reflection is a very useful tool and if you aren’t familiar with the state of affairs in simple C++.

The cmake-reflection-template repository is a small working example of a few source files with added reflection which generates serialization and deserialization routines (using std::any<> for simplicity – so it requires C++17 – but it can be rewritten to serialize to JSON instead).

• Each CMake target that wants to have reflection should have the target_parse_sources() CMake function called on it like so
• Each source file in the reflected projects has an attached custom CMake command so when it gets modified that command gets ran
• That command runs the parser on the file – named for example my_type.h – which generates code and dumps it in a file called my_type.h.inl in a gen folder inside CMAKE_BINARY_DIR
• The resulting my_type.h.inl can be included either directly in my_type.h or perhaps elsewhere – the forward declarations of the generated functions are written inside the classes in my_type.h using the helper FRIENDS_OF_TYPE(MY_TYPE); macro.

It is a bit like what Unreal is doing for reflection of properties – C++ source code is parsed (and annotated with preprocessor identifiers) and each source file includes the generated code for itself.

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Modules are coming in C++20 but it will take a while before they are widely adopted, optimized and supported by tooling.

Release of CMake 3.16 does not require resorting to 3rd party CMake scripts from GitHub for precompiled headers and unity builds:

• To precompile means that the compiler will parse the C++ headers and save its intermediate representation (IR) into a file, and then when compiling the .cpp files of the target that IR will be prepended to them – as if the headers were included – the contents of the PCH are the first thing each translation unit sees

• Easy to integrate – doesn’t require any C++ code changes
• ~20-30% speedup with GCC/Clang (can be up to 50%+ with MSVC)
• For targets with at least 10 .cpp files (takes space & time to compile)

What to put in a PCH

• STL & third-party libs like boost (used in at least ~30% of the sources)
• Some rarely changing project-specific headers (at least 30% use)
  • for example if you have common utilities for logging/etc.
• Each time any header which ends up in the PCH is changed – the entire PCH is recompiled along with the entire target which includes it
• Careful not to put too much into a PCH – once it reaches ~150-200MB you might start hitting diminishing returns
• How to determine which are the most commonly used header files
  • option 1: do a few searches in the codebase/target
    • <algorithm>, <vector>, <boost/asio.hpp>, etc.
    • note that some header might be included only in a few other header files, but if those headers go everywhere, then the other header gets included almost everywhere as well
  • option 2: – use software to visualize includes & dependencies

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