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by kamov 603 days ago
Rust used to have a GC in the past, as well as green threads and a bigger runtime. All of this has been explicitly removed before Rust 1.0. The reasons are well documented in many pull requests and RFCs for the language.

The way the async feature works in Rust is that the asynchronous function is just a syntax sugar that gets desugared into a state machine struct during compilation. The way this state machine works is similar to how one could achieve async in a language like C. It's unfair to dismiss everything as excuses given that the fundamental aim of the language is different.

In Rust async functions are not really colored because again - the async function is just a syntax sugar for a struct you can create and use in a sync context. The colors analogy is only really applicable in a language like JavaScript, where there's no way to poll an async function in a sync context.
1 comments
adastra22 603 days ago
Here's the thing though: Rust could have every function be an async state machine, automatically. And then the compiler optimizes away that code when it isn't needed. It would be a big pain to implement, but it's doable, and it would deliver a developer experience much closer to Go's. There isn't a technical reason for why Rust couldn't do this.

FYI you can't poll an async result in a sync context in Rust, either.

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Ygg2 603 days ago
> There isn't a technical reason for why Rust couldn't do this.

First, it would be a huge undertaking. That in itself is a huge time/resource burden.

Second, it would add overhead to any non-async function call. Because async introduces branching on every function invocation, it would make the resulting assembly even harder to understand. This strongly goes against the zero overhead/ zero cost abstraction idea of Rust.

By the same measure, Go could technically remove (almost) all GC, add some kind of borrowing mechanism and steal Rust's thunder.

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dwattttt 603 days ago
> FYI you can't poll an async result in a sync context in Rust, either.

Sure you can. Async runtimes in Rust are written in Rust, that's exactly what they do.

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