[adastra22]

(1) Higher order functions are pretty much the same as all the other languages you mentioned, using closure syntax? What was the problem you ran into?

(2) In such situations the compiler (type system or borrow checker) is telling you that what you wanted to do has hidden bugs, and therefore refuses to compile. Usually that's a good thing.

(3) &dyn Trait

[Darmani]

(1) Oh sure, the syntax is easy. Getting it to borrow-check is somewhere between insane and impossible. As I said, I've had friends who are actual Rust experts give up trying.

(2) No, it stems from a compiler limitation (imposed in large part by the need for static memory layout), not because there's anything intrinsically buggy about doing this.

(3) Look up "dyn-compatibility", for the largest, but not the only, problem with doing this.

[yobbo]

If your goal is to translate Haskell (or other garbage collected code) pattern-for-pattern into Rust, you will almost certainly burn out.

[Darmani]

It seems to be a common reflex of Rust advocates that, whenever an issue with using the language is asked about, the response is "That's just a garbage-collected code pattern" followed by "and therefore you shouldn't want it." It's happened multiple times in this thread. [Edit: and both the times I was thinking of were from you, so need to weaken that conclusion]

Aside from having vibes of "I've chosen to get hit weekly in the face with a baseball bat, but have learned to like it, and so should you" it's also seldom true.

All three of these examples are also quite easy to do with C and C++. It's not about garbage collection.

[Boxxed]

"It's possible to write <lang-X> in <lang-Y>" is a common trope, but "It's possible to write <lang-X> in Rust" is painful and borderline impossible in my experience. I don't mean this as a defense of rust, I just think it's why the learning curve is so harsh.

[adastra22]

Rust makes you be explicit about memory management. I guarantee you if you threw everything into a box inside an Arc, your copy closures would have still worked just fine and your Haskell idiom would translate cleanly. Only now everything is heap allocated and reference counted. Before LLMs took over the reins, this was the hallmark of beginner rust code because it WOULD work, just with unnecessary allocations and copying and pointer dereferencing.

Rust makes the tradeoffs explicit, and Rust programmers tend to obsess over minimizing those tradeoffs to get abstractions that are zero-cost. So doing it “the rust way” is often very complicated and tricky to get right while satisfying the borrow checker and type system, but once found is lean, fast, clean, and safe.

[Darmani]

Oy. It is also a common experience that, when I struggle in Rust to use a pattern that's common in nearly every other language or find another way to achieve the same goal, people who know of my Haskell background call it a "Haskell pattern," and thereby avoid facing the suggestion that their favorite language is missing some pretty basic affordances.

No, boxing everything does not magically make things more dyn-compatible. It will not magically solve the issue that tokio does a whole-program transformation that does its most restrictive checking only after all local checks have been resolved. It will not magically allow more reuse between datatypes. It will solve none of the problems I encountered... because if beginner-Rust could solve any of these problems, then they would have ceased to be problems for me by the time I became intermediate.

> Rust programmers tend to obsess over minimizing those tradeoffs to get abstractions that are zero-cost. So doing it “the rust way” is often very complicated and tricky to get right while satisfying the borrow checker and type system, but once found is lean, fast, clean, and safe.

You and I must be using very different definitions of "lean." For me, "complicated" and "lean" do not go together

[adastra22]

I am sorry that Rust isn't for you. There is beauty in a systems programming language, but you have to be willing to think as a systems programmer. That's not for everybody.