RFC: scope and borrowing

[via Digitalmars-d]

On Sunday, 21 September 2014 at 03:39:24 UTC, Walter Bright wrote:
> I think it's a well thought out proposal. Thanks for doing this!
>
> A couple thoughts:
>
> 1. const can be both a storage class and a type constructor. 
> Scope is only a storage class. The scope(int) syntax implies 
> scope is a type constructor, too.
>
>     const int* a;  // const used as storage class
>     const(int*) b; // const used as type constructor
>
> The type constructor syntax should be disallowed for const.

(... disallowed for _scope_, I assume)

I originally intended it to be part of the type. Ivan Timokhin 
pointed out severe problems with that [1], so I removed it from 
the proposal. The syntax is a remainder of that.

But before I remove it too, I have a question: Will it still be 
possible to use the storage class syntax for members of 
aggregates?

     struct S {
         scope!myAllocator int* p;
     }

>
> 2. I think there is quite a bit of overlap between scope and 
> ref. Essentially, ref does everything scope does, except deal 
> with classes. I'm not terribly comfortable with such a large 
> overlap, it implies something is wrong. I don't have an answer 
> at the moment.


I also see the overlap, but there are also large differences to 
the point that I cannot see how the two concepts could be 
unified. For one, `ref` with classes (and reference types in 
general) is troublesome, and would introduce a double indirection 
for borrowing, when a simple copy of the reference would be 
sufficient. Then, `scope` could also for non-reference types. 
File handles come to mind, which are often integers, and just 
need to be copied.

[1] 
http://forum.dlang.org/thread/etjuormplgfbomwdrurp@forum.dlang.org?page=3#post-lusirm:2421d9:241:40digitalmars.com