Comment by stevefan1999

4 days ago

I hate to say it (and I know a lot of C apologists will downvote it), but there is no native closure in C, all you have is a function pointer in C, and you need to manually add the "context" pointer to make it a closure, in the strict (textbook) sense. That's because C does not have the concept of "data ownership", only automatic memory (that is on stack or register) or manual memory (in the sense of malloc/sbrk'd blocks), but a (again, textbook definition of) closure requires you to have access to the data of caller/"parent"/upper layer [^1].

And that's why I generally don't see C to have closures, and requires a JIT/dynamic code generation approach as this article has actually done (using shadow stacks). There is also a hack in GNU C which introduce local function lambda, but it is not in ISO C, and obviously won't in the next decade or so.