[Hirrolot]

Closures in Rust are fundamentally broken. See [1] for the discussion.

[1] https://hirrolot.github.io/posts/rust-is-hard-or-the-misery-...

[burntsushi]

Lol. "fundamentally broken" and yet I've been using them with little to no friction for pretty close to a decade now. If that's what you think "broken" means, then, well, you've completely devalued the word. This right here is what we call sensationalism folks.

Now if you said, "Rust has some rough points at the intersection of generics, closures and async programming," I'd say that's absolutely true!

[Hirrolot]

> "fundamentally broken" and yet I've been using them with little to no friction for pretty close to a decade now.

This might rather confirm my point, since engineers using a specific programming language quite often have a contorted picture of how code in other languages is written, as they become more and more acquainted with their main tool. If we compare Rust closures with those of ML languages, it becomes pretty clear how natural closures are in ML and tricky in Rust.

Not quite a sensation either to anybody who happened to use closures in a typical Rust code, which, apparently, happens to have quite a lot of generics and async!

[burntsushi]

The sneer is strong with this one.

> This might rather confirm my point

It might, but it doesn't, because I don't only use Rust. Notice also how you've moved the goalposts from "fundamentally broken" (sensationalist drivel) to "how natural closures are in ML and tricky in Rust" (a not unreasonable opinion with lots of room to disagree on the degree of "natural" and "tricky").

[pitaj]

That's not just closures, but a confluence of closures, async, and more.

[Hirrolot]

The example provided in the post -- yes. But I can basically demonstrate other language features that are not working with closures, such as generics -- you just can't have generic closures in the same way as you have generic functions, even in a synchronous code. With closures, you have a pretty limited scope of what you can do, considering the rest of the language, so I think it'd be pretty useless to consider closures as a separate mechanism that shouldn't interact with the rest of the language.

[burntsushi]

> But I can basically demonstrate other language features that are not working with closures, such as generics -- you just can't have generic closures in the same way as you have generic functions, even in a synchronous code.

Generics and closures work just fine:

    use std::ops::Add;

    fn adder<T: Copy + Add<Output=T> + 'static>(x: T) -> impl Fn(T) -> Box<dyn Fn(T) -> T> {
        move |y| Box::new(move |z| y + x + z)
    }

    fn main() {
        let add23 = adder(2)(3);
        assert_eq!(10, add23(5));
        assert_eq!(13, add23(8));
    }

You keep making sensationalist generalizations. It's trivial to demonstrate that closures and generics work together just fine, as I've done above. Are there subtleties and complexities and other things that can make certain cases or areas tricky? Absolutely. But that's not the same as "not working."

[Hirrolot]

Well, your example is not a generic closure, since inside `adder`, you already have a generic type `T`; it's introduced by the `fn` keyword. If we try to do the same for a closure, we would face a type error. This issue has been discussed on SO [1].

I haven't claimed that closures are not working, since well, they are working, but under a very limited set of circumstances. Again, I see nothing sensational, since the trickery of using closures has been discussed elsewhere.

[1] https://stackoverflow.com/questions/34814423/possible-to-def...

[burntsushi]

> Well, your example is not a generic closure, since inside `adder`, you already have a generic type `T`; it's introduced by the `fn` keyword. If we try to do the same for a closure, we would face a type error. This issue has been discussed on SO [1].

Of course it's generic. If you were to write the type out for the closure, it would be generic over 'T'. (Whether that type ever actually gets written out that way or not is a different matter.) As far as I can tell, what you're saying is that Rust doesn't support higher-rank polymorphism. Which is true (for types, but not for lifetimes). But that's not the same as "generics don't work with closures."

> I haven't claimed that closures are not working

You've said:

> Closures in Rust are fundamentally broken.

(which was completely unqualified and not to a "very limited set of circumstances")

and (emphasis mine)

> But I can basically demonstrate other language features that are not working with closures, such as generics