"Semi-const" methods?

[Mafi]

Am 13.03.2011 23:27, schrieb Magnus Lie Hetland:
> I have a data structure that's generally static (const, or even
> immutable), but it has some utility storage, which caches certain
> results during use. This caching etc. doesn't really affect the
> semantics of the main object, and are reset between operations, so I
> think it still would be useful to declare (and statically check) that
> certain methods don't modify any of the *rest* of the structure (i.e.,
> the "main parts").
>
> I *could* declare the methods const, and pass in a second object (a
> non-const parameter) for the caching etc. Or I cast the relevant parts
> to const (assigning them to local variables) early on in the relevant
> methods (dropping the const modifier on the method itself -- sort of a
> bummer).
>
> Any other ideas on how to handle this sort of "mostly const" or "const
> where it counts" stuff? Perhaps my design intentions here are off to
> begin with?-)
>

I found away which doesn't use casts or bugs.
Just use delegates/closures.

class C {
	int i;
	int delegate(int) getCache;

	this(int fi) {
		this.i = fi;	
         int lastX, lastR;
		this.getCache = (int x) {
			if(x == lastX) return lastR;
             lastX = x;
             lastR = x * i;
             return lastR;
		};
	}

     const multiply(int x) {
         return getCache(x);
     }
}