@safe leak fix?

[Jason House]

Walter Bright Wrote:

> Consider the code:
> 
>    @safe:
>      T[] foo(T[] a) { return a; }
> 
>      T[] bar()
>      {
>          T[10] x;
>          return foo(x);
>      }
> 
> Now we've got an escaping reference to bar's stack. This is not memory 
> safe. But giving up slices is a heavy burden.
> 
> So it occurred to me that the same solution for closures can be used 
> here. If the address is taken of a stack variable in a safe function, 
> that variable is instead allocated on the heap. If a more advanced 
> compiler could prove that the address does not escape, it could be put 
> back on the stack.
> 
> The code will be a little slower, but it will be memory safe. This 
> change wouldn't be done in trusted or unsafe functions.

At a fundamental level, safety isn't about pointers or references to stack variables, but rather preventing their escape beyond function scope. Scope parameters could be very useful. Scope delegates were introduced for a similar reason.