Type Safe Generic Data Structures in C

See my follow-up article: "A Fast, Growable Array With Stable Pointers in C"
I write type safe generic data structures in C using a technique that I haven't seen elsewhere1. It uses unions to associate type information with a generic data structure, but we'll get to that. My approach works for any type of data structure: maps, arrays, binary trees… but for this article I illustrate the ideas by implementing a basic linked list.