STC VS ctl

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.

C Container Template Library (CTL)

I guess something like that may exist but it can be done with the preprocessor alone. See https://github.com/tylov/STC or https://github.com/glouw/ctl

I assume you refer to that two of the letters match with STL or STD, right? Even if they are not related to C at all. I assume STB, CTL, are not acceptable for you either?

The standard C library lacks any kind of containers (vectors, hash tables etc.) so the first thing would be to find one you like. For example, the C Template Library is a nice one: https://github.com/glouw/ctl

While I agree the common pattern is to use void*/dynamic dispatch, this is not necessary. E.g., https://github.com/glouw/ctl/ or https://github.com/c-blake/bst show a couple ways to have generic code statically specialized in regular old C.

The template instantiation is rewritten and is now similar to how glouw CTL library does it. STC no longer contains long macros for generating the templated code.

define type macros before #including the implementation. (intrusive) This is how https://github.com/glouw/ctl does it. The good: type-safety. no casting, clear error messages. Somewhat clumsy to have to individual #includes for each container type instantiation of the same container.