[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!