Proposal for design of 'scope' (Was: Re: Opportunities for D)

[via Digitalmars-d]

On Thursday, 10 July 2014 at 20:10:38 UTC, Marc Schütz wrote:
>     struct S {
>         int* p;
>         void releaseBuffer() scope {
>             // `scope` in the signature applies to `this`
>             free(this.p);
>             this.p = null;
>         }
>     }
>     int bar(scope ref S a, scope int* b) {
>         a.releaseBuffer();
>         return *b; // use after free
>     }
>     S s;
>     bar(s, s.p);
>
> The root cause of the problem here is the call to `free()`. I 
> _believe_ the solution is that `free()` (and equivalent 
> functions of allocators as well as `delete`) must not accept 
> scope parameters.

Thinking more about it:

     struct S {
          int* p;
          void releaseBuffer() scope {
              free(this.p);
              this.p = null;
          }
      }
      int bar(void delegate() a, scope int* b) {
          a();
          return *b; // use after free
      }
      S s;
      bar({ s.releaseBuffer(); }, s.p);

So, for what I suggested (`free()` mustn't accept scope) to work, 
an additional rule is required: While a borrowed reference exist, 
the original must also be treated as scope.

Now, this is much more complicated to implement :-( Maybe there's 
a better way?