Update on await syntax in Rust

Post by steveklabnik » Tue, May 28, 2019, 6:16 PM UTC

mdpopescu wrote: post #90

Nican wrote: post #71

Earlier quoted context omitted.

For example, on C#, I sometimes have to do: var value = (await (await startRequest()).GetBody()).Root; While the Rust syntax would make this a little more clear, I do not think it is a dealbreaker.

Please don't do that. I had to look several times to rewrite it as var temp1 = await StartRequest(); var temp2 = await temp1.GetBody(); var value = temp2.Root; which is instantly grokked.

Post by staticassertion » Tue, May 28, 2019, 6:24 PM UTC

steveklabnik wrote: post #93

numakerg wrote: post #84

Earlier quoted context omitted.

Why couldn't they use a macro or a function? EDIT: nvm. it says in TFA not the linked writeup

It cannot exist as a macro or function, because it transforms the code in ways they can’t. Macros can transform code, but the final output isn’t something representable in stable Rust, and so it would not compile post-expansion.

Post by oconnor663 » Tue, May 28, 2019, 6:27 PM UTC

ben509 wrote: post #59

steveklabnik wrote: post #27

Earlier quoted context omitted.

> I'm interested to know how much of this was a religious battle and how much of it results in meaningful complications for user code down the line. Due to the connotations of "religious battle", it's hard to get a good answer here. Nobody wants to be painted in this light. > Is this syntax for native coroutines? No. > Can it be combined with existing user and stdlib syntax? Yes. > What pathways for syntax developmen…

> Due to the connotations of "religious battle", it's hard to get a good answer here. Nobody wants to be painted in this light. Haven't we all found ourselves lined up as one of a pair of camps over some heated dispute over a bit of minutiae? The whole time you know it's a bit silly, but not entirely and you feel compelled to continue to argue. Using a term like "religious battles" with tongue firmly in cheek is reco…

Post by eridius » Tue, May 28, 2019, 6:29 PM UTC

kibwen wrote: post #82

Nican wrote: post #71

Earlier quoted context omitted.

For example, on C#, I sometimes have to do: var value = (await (await startRequest()).GetBody()).Root; While the Rust syntax would make this a little more clear, I do not think it is a dealbreaker.

For ease of comparison, here's how that would look with syntax akin to Rust's choice: var value = startRequest().await.getBody().await.Root;

  var value = startRequest.await?.getBody().await?.Root;

Post by steveklabnik » Tue, May 28, 2019, 6:30 PM UTC

nemothekid wrote: post #102

steveklabnik wrote: post #101

Earlier quoted context omitted.

This is a great example of why syntax and semantics can't be separated. This works great in GC'd languages, but in Rust, these two things may not be equivalent. With the distinction between owned and temporary values, this may change the lifetime of what stuff is in scope and when. This is reduced a bit with non-lexical lifetimes, but it's not, strictly speaking, actually equivalent.

I think this is a good example to show people who are on the fence about postfix then. I haven't felt strongly about postfix, but this is an eye opener for me.

    fn main() {
        let world = gives_string().split(" ").next();
        
        println!("{:?}", world);
    }
    
    fn gives_string() -> String {
        String::from("hello world")
    }

    fn main() {
        let world = gives_string();
        let world = world.split(" ").next();
        
        println!("{:?}", world);
    }
    
    fn gives_string() -> String {
        String::from("hello world")
    }