[sanderjd]

Honestly, I think syntax for Arc (and/or Rc or some generalization of the two) and more "cultural" support for writing in that style would have benefitted rust back when 1.0 was being finalized. But I think the cow is out of the barn now on what rust "is" and that it isn't this.

[cmrdporcupine]

Yes, if you think about it, it's a bit weird that async gets first syntactical class treatment in the language but reference counting does not. A similar approach of adding a syntactical form but not mandating a particular impl could have been taken, I think.

Same for Box, but in fact Rust went the opposite way and turfed the Box ~ sigil.

Which I actually feel was a mistake, but I'm no language designer.

[zozbot234]

Async has to get first-class treatment in the syntax because the whole point of it is a syntax-level transformation, turning control flow inside out. You can also deal with Future<> objects manually, but that's harder. A special syntax for boxed variables adds nothing over just using Box<> as part of the type, similar for Rc<> (note that in any language you'll have to disambiguate between, e.g. cloning the Rc reference itself vs. duplicating its contents, except that Rust does it without having to use special syntax).

[sanderjd]

Yeah, but personally I think Rc/Arc is more deserving of syntax than Box!

[steveklabnik]

A long time ago, it did have specialized syntax! We fought to remove it. There’s a variety of reasons for this, and maybe it would make sense in another language, but not Rust.

[sanderjd]

For Arc/Rc? I don't recall that! What was it? I recall it being `&borrowed`, `~boxed`, `@garbage_collected`.

Aaaah, I'm realizing in typing this that the `@foo` syntax was actually implemented via reference counting? I think my intuition at the time was that the intention was for those to eventually be backed by a mark-and-sweep GC, which I did think was a poor fit for the rest of the language. But as just a syntax for reference counting, I honestly think it might have been an ok fit.

Or maybe not, I'm ambivalent. But the syntax thing in my comment is more of a red herring for what I think is more of a cultural "issue" (to the small extent it is an issue at all), which is that most Rust projects and programmers seem to try to write in a style that defaults to only choose reference counting when they must, rather than using a style of optimizing them out if they show up in a hotspot during profiling.

[steveklabnik]

Yes, I’m referring to @foo, which IIRC maybe in the VERY old days had a GC but from when I got involved in 2012 was reference counting, iirc.

Regardless of the specifics here, the same problems apply. Namely that it privileges specific implementations, and makes allocation part of the language.

[sanderjd]

Yeah, which circles back to the thread-starter's comment. My thought-experimental different version of rust would not mind shipping with a privileged implementation of garbage collection, or having allocation be part of the language.

It wouldn't be a good fit for projects like the ones at Oxide :) I'm very glad Rust itself exists, with good support for use cases like those!

[iopq]

@gc references were Arc under the hood!

[sanderjd]

Totally makes sense! Not sure if I never knew or if that knowledge got lost in the sands of the past decade (or more, I think?) of time.