STC VS CommonC

This technique is often used to implement RAII in C. See example in Standard Template Containers. The library delivers STL-like functionality to C.

I'd say it's evil, but quite understandable very commonly used because there are no built-in alternatives in C. I basically never use void* in user-code, simply because there are no need for it when using a templating technique, like in my STC library. Even in the implementation of STC itself, void* is hardly used, if at all.

Study Other Peoples C Code and here's one that is easy to read: https://github.com/stclib/STC/releases

STC

This is more or less how C-ish templates are implemented in STC library.

As the author of a STL-like templated C container library, I had many of the exact same thoughts when implementing the unordered map. In fact, I also changed to many of the suggestions here, rather than consistently following the C++ umap API. E.g.

Sure it is. C misses a proper efficient generic standard/container library, like my https://github.com/stclib/STC, but that is irrelevant.

Smart Template Containers (STC)

Some data structure and algorithm library in C enable the (optional) separation between the interface of the container (which is expanded in your header) and its implementation (which is expanded in your source), like STC.

Now for that disgusting pile of steaming hot spaghetti, the implementation itself. Basically the macros used are defined across a number of headers: Hacks.h (not everything is relevant here, mostly the stuff to do with counting, retrieving last arg, maps, etc.), Generics.h, Generic.h (this will probably be renamed to Generic1.h as it’s only used for single parameter templates generics), and finally Template.h which is where most of the heavy lifting is being done. So yeh, it’s disgusting but it works... but it’s disgusting. So please please please no one think about using it, it will without a doubt make your life miserable (and it will make my life miserable if I have to support this) as it’s almost a guarantee that there’ll be use cases that haven’t been handled and most likely has tons of bugs hiding in that mess.