Why D const is annoying

[Mehrdad]

> > Wouldn't "physical" const-ness be an implementation detail of the 
> > object, and therefore, impossible to determine by the user of the 
> > object?
> No, it's not an implementation detail. When you mark an object as being 
> physically const, then you're guaranteeing that you will not alter it 
> through that reference or pointer.

I think you misunderstood my question.

Yes, __IF__ you mark an object as physically const, then the world is 
beautiful...

My question is, __WHEN__ can you ever do that, except in the most trivial 
situations?
As soon as you try to add an extra layer of indirection (be it a proxy, 
implementing a method in an interface, overriding a base class method, 
etc.), there is NO WAY for the caller to know what obj.foo() does on obj. 
How can it possibly know whether obj will stay physically const?