naivete
Nothing about C is easy or logical. C only makes sense in 1965 on PDP7. All these hacks just work around the inherent shittyness of C/C++.
Just for context, in C++ including std::string (after preprocessing) will pull in 25k LoC, std::vector around 20k.
Programming in C++ by the book will average around 35k LoC per every compilation unit. And it will compile significantly slower than C code.
Having that in mind, and considering that Nuklear doesn't pull in any dependencies, not even C stdlib parts. I think author has done a good job at being lean and fairly straightforward.
UI libs are usually a huge dependency and a hairy mess. This is not really the case. It's just one ~1mb 20k line header file.
There is some overhead on preprocessing over having a .c/.h combo, but that's it.
What's the C preprocessor speed of GCC/Clang/MSVC? Any benches?