Lately on another Rust thread somebody pointed out that C programs use a lot of indirection like pointers and vtable dispatches which actually detracts from the supposed mega-speed of the low-level C. I found that to be mind-blowing and felt stupid for not remembering that earlier.
I think they meant function pointers in general (callbacks and the like, see qsort). Also, a lot of C codebases end up implementing manual vtables of some sort where polymorphism is required.
It's true they aren't that common, but have you looked at the Linux kernel code? It's written in C, and vtables are everywhere.
I've also used them on occasions. They do a particular job people call pluggable implementations / dynamic typing / sub-classing depending on their background. If there isn't some central place that knows all the types (if there is you can use switch/case/match), there isn't much choice, it's vtables or nothing. But needing to do that job is rare, so seeing it in languages that don't use vtables promiscuously to implement OO is correspondingly rare.
Which is as it should be, because vtables are more expensive than a direct call, very expensive if they prevent inlining. One of rust's triumphs is it provides them, but you have to go out of your way to use them so it encourages avoiding their overheads.
Dynamic dispatch (vtables are one way to do it, and so is a function pointer) is incredibly common in C, because there's no language-built-in way to perform monomorphization.
