[rust-dev] "let mut" <-> "let !"

Patrick Walton pcwalton at mozilla.com
Fri Jan 31 20:27:06 PST 2014

On 1/31/14 8:24 PM, Eric Summers wrote:
> I’m new to Rust (three days), but I thought the mut syntax felt odd in a few places.  Type definitions in particular because it is one of the few places that require padding.  Is there any reason a symbol isn’t used for mutability instead?  Forgive me if I’m too naive in Rust.
> With a symbol you can drop the space:
> fn drop(&mut self) { .. } <-> fn drop(&!self)
> The only other common situation I've seen so for that require the space are lifetime annotations.  Maybe there is an alternate form for those?
> The symbol could probably be extended to let:
> let mut a = 0; <-> let !a = 0; <-> let a: !u32 = 0;
> or maybe mutable setter;
> let a := 0;
> As other said, I think ‘var' sugar feels against the design of the language.

     let !a = 0 is ambiguous with macros. (cf. `let! a = 0;`)


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