Code from yalsat (stochastic SAT solver) [1] made me learn something two years ago. I can declare an array of some elements and make access to elements statically typed. Same with maps, sets and others.
this is a pointer-based language so there are lots of ways to solve that, but you know that already.. this is a setup question.. of course its not useful to re-invent critical, secure functions over and over yet, what if I am not writing critical, secure functions anyway?
I would choose a key type that is natural to the environment and problem.. unsigned integers are useful. Which unsigned integer size? there are only a couple of practical answers to that.. unless there is some massive dataset, use a 32bit unsigned integer, like so much of the software does right now.
Type safety and encapsulation aren't the same thing. Encapsulation is about hiding implementation details from the user of an API, which is what the comment I originally replied to was claiming you couldn't do in C.
The void * is (should have been!) an implementation detail, and you're leaking it in the interface - that's not encapsulation.
For example if I want to store a __int128 on a 64-bit machine I'll have to deal with stuff like memory allocation and lifetime myself, when the data structure should do that.
It's not an implementation detail, it is part of the interface. The data it points to belongs to the caller and the caller is responsible for managing it, just like anywhere else in C.
> The data it points to belongs to the caller and the caller is responsible for managing it
Going back to the start of the thread where you said you didn't understand this:
> this means that using, say, a dictionary means that quite a bit of the implementation gets hard coded into every site that uses the dictionary
You can see you've just said yourself what you were saying you didn't understand - with data structures in C you're responsible for manually managing things that the data structure would via things like generics in most other languages, with you having to instead hard-code them at the use-site to turn the data into something that can be pointed to and managing the lifetime.
When you write a set function for your map data structure, what type do you make the key parameter?