RFC: scope and borrowing

[via Digitalmars-d]

On Saturday, 4 October 2014 at 18:13:03 UTC, Ivan Timokhin wrote:
> On the second thought, doesn't syntax look a bit awkward now? I 
> mean, `scope!a(T)` certainly looks like `scope!a` as a whole is 
> a type modifier. Since this syntax is pretty much limited to 
> function return types with this proposal, maybe a better 
> solution would be to have an owner as a separate annotation on 
> a function?

I agree, but it should still stay closely associated to the 
return type.

>
> Also, would it really make much sense to track the owner 
> further than the assignment of a function's return value? That 
> seems to complicate things a lot by adding a hidden attribute 
> to a variable that is not only invisible at the declaration 
> (even though the full type is spelled out), but, in fact, 
> cannot be specified explicitly (because there's no syntax for 
> that, now that scope with owners is limited to function 
> signatures).
>
> How about this:
> ---
>     scope(string) haystack, needle;
>     // next assignment is okay, because `s` is guaranteed not 
> to outlive
>     // `haystack`.
>     scope(string) s = findSubstring(haystack, needle);
>     // type of `s` is now scope(string), no additional 
> information
>     // attached
>
>     // so the next assignment is disallowed:
>     //needle = s; // error!
> ---
>
> This could be unnecessarily limiting, but would it really cause 
> much trouble?

I think you're right, I thought about this after I replied to 
you. It would be the logical next step. On the other hand, I 
wouldn't want to lose const borrowing, because it turned out to 
be a requirement for safe moving. But I think it can still be 
tracked internally (owner tracking is necessary for 
implementation anyway).