const?? When and why? This is ugly!

[Burton Radons]

Walter Bright Wrote:

> Burton Radons wrote:
> > This wouldn't be too bad because const is worthless when optimising,
> > but if invariant is going to be given any weight then we must never
> > cause data to be casted to invariant unless if it's actually
> > invariant data. So, the sensible default is "const (char) []" for
> > strings, a selection of aliases in object.d for the others, and safe
> > casting templates in object.d.
> 
> What I interpret from this is that you see strings as fundamentally 
> mutable character arrays, and sometimes in special cases you can make 
> them immutable. I propose turning that view on its head - regard strings 
> as fundamentally immutable, and having a mutable char array is a rare 
> thing that only appears in isolated places in the program.

No, I don't. You are misunderstanding me, and I'm not sure why or how. Here's a (contrived) example of where my concern may come into play:

   int [] a = new int [1];

   a [0] = 1;

   auto b = cast (invariant (int) []) a;

   a [0] += b [0];
   a [0] += b [0];
   writef ("%s\n", a [0]);
   // Normal result: 4.
   // Optimiser which assumes invariant data can't change: 3

Yes, the code is an abuse of the const system. THAT'S EXACTLY MY POINT. Casting mutable data to invariant leads to situations like these. Only data which will never change can be made invariant. Putting "alias invariant (char) [] string" in object.d induces these situations and makes it seem like it's a good idea.