const again

[Walter Bright]

Steven Schveighoffer wrote:
> "Walter Bright" wrote
>> Steven Schveighoffer wrote:
>>> What happens if you have this?
>>> const(T)*[]
>> Array of pointers to constant T.
>>
>>> If T is a struct, then it's fine, but if it's a class, then what?  To me 
>>> the situation is just as bad.
>> It is perfectly consistent. I don't see why it is bad.
> 
> const(T)*[] x;
> 
> x[0].member is a struct member if T is a struct, what is it if T is a class? 
> I was under the (possibly wrong) impression that this is illegal?

I don't understand. Exactly what is illegal?


> Sure, but your original point was to be "able to wrap any type with a 
> struct, and have it be possible for that
> struct to behave as if it were that member type".  I believed you were 
> implying that this was a reason NOT to have a & operator.  My question to 
> you is, how does having a reference operator make this more difficult than 
> not having one?  A reference is a pointer.

There's the problem we're having. While a class reference is implemented 
as a pointer 'under the hood', to the type system, it is not a pointer.


> OK, I am confused, isn't const(S)* tail const?

No. For const(int*), tail const of that construct would mean that the 
pointer is mutable while what it points to is not.


> And if so, how does this new 
> scheme rid us of tail const?

It would say that const(int*) would mean an immutable pointer to an 
immutable int.

> Couldn't I use this to call a const member 
> function on a struct?

I'm very confused as to what you're referring to.


> The way I am interpreting your new const is that I can have tail-const for 
> struct references (pointers) but not tail-const for class references.

No. The correct interpretation is that all parts of the type within the 
( ) are immutable.


> In other words, I can create a tail-const struct array via:
> 
> const(S)*[] tailconst;
> tailconst[0] = new S; // ok to assign to tailconst[0]
> tailconst[0].nonconstfunc; // error, cannot call const function
> 
> How do I do the same for a class?

You cannot separate the class reference from the class fields.