This isn't complex. It's a bit unusual, but not hard to understand if you understand the basics of how #include and #define work.

If you're working on the sort of C++ codebase that would benefit from this sort of code generation, and you're not reasonably skilled in C++, then god help you.

Are you talking about the X macro itself, or more generally?

I may be the obtuse one here, but for a more complex example, it took me a few hours to manage to make nested loops using Boost PP (for explicit instantiations). Even so, I avoid having to write a new one that's not a quick copy-paste because it's quite different from usual C++ programming, so my painfully acquired understanding quickly evaporated... as I suspect is the case of anyone who doesn't particularly focus on the C prepro.

In the end, it's just simpler to get some Python script or C++ program to write a string and dump that to a file than to write something illegible with the C preprocessor, if doing something at all complicated (in my opinion).

I'm talking about X-macros. There's a wide range of preprocessor shenanigans, from "everybody needs to know this" to "oh my god why." Each construct needs to be evaluated on its merits. IMO X-macros are closer to the simpler side of that spectrum. Consider writing things out by hand if you just have a few, but if you have a lot of things repeating like this, they're a fine tool to use. Boost PP is a whole different level of ridiculousness and I don't see ever using that sort of thing for anything serious.