> - static reference counting (no GC, like in Rust, but with no borrowing and borrow problems);
Does this mean that it's somewhat equivalent to Rust with everything behind a `Rc` or `Arc`?
Does this mean that it's somewhat equivalent to Rust with everything behind a `Rc` or `Arc`?
But Roc counts references in _compile_ time. So it's like _usual_ (not wrapped in Rc<>) values in Rust. But in Rust the value is deleted from the heap when the stack frame with the _only_ link to it («the owner») is deleted. And in Roc the value is deleted from the heap, when the _last_ link to it leaves the stack.
So we have the machine code _almost_ as efficient as a Rust-produced machine code, but the source code with a much simpler semantics.
Example: A linked list.
Nitpick: Rc and Arc are not traits.
See also Anton Felix Lorenzen's master thesis: https://antonlorenzen.de/master_thesis_perceus_borrowing.pdf
Mr. Feldman also mentioned some «alias analysis» library «Morphic Solver» from Berkley University, but I cannot find anything about it.
BTW compile time reference counting was already discussed on HN, for example here: https://news.ycombinator.com/item?id=19567666
> Example: A linked list.
IIUC recursive data structures like linked list and trees are not the problem for the static reference counting. Mutation (and, therefore, link cycles) _is_ a problem, but Roc is a clean language with no explicit mutation. =)
> I can see so many basic cases in which it doesn't work
Sometimes runtime reference counting is still used. But, of course, in way more complex situations than just processing a linked list.
> Nitpick: Rc and Arc are not traits.
Of course, my fault. I haven't written on Rust for a long time (and never used this language in a serious project).
edit: link added
It's an another experimental programming language with the static reference counting. «Morphic uses a borrow-based reference counting scheme which is able to eliminate almost all reference count increments and decrements for a large class of programs»ⓒMorphic developer team.
I think I've read a post by Niko Matskakis (Rust lead) who suggested doing something similar. That would be exciting to see!