[starspangled]

> You can take it a step further:

No, that is essentially what Linux does in this article (and by the looks of it also ffmpeg).

struct file does not have a bunch of pointers to functions, it has a pointer to a struct file_operations, and that is set to a (usually / always?) const global struct defined by a filesystem.

As you can see, the function types of the pointers in that file_operations struct take a struct file pointer as the first argument. This is not a hard and fast rule in Linux, arguments even to such ops structures are normally added as required not just-in-case (in part because ABI stability is not a high priority). Also the name is not mangled like that because it would be silly. But otherwise that's what these are, a "real" vtable.

Surely this kind of thing came before C++ or the name vtable? The Unix V4 source code contains a pointers to functions (one in file name lookup code, even) (though not in a struct but passed as an argument). "Object oriented" languages and techniques must have first congealed out of existing practices with earlier languages, you would think.

[rzzzt]

The proto-C++ transpiler used C with this and similar techniques behind the scenes: https://en.wikipedia.org/wiki/Cfront