Re: [sv-ec] classes questions

Arturo,

I am somewhat Ok with allowing things like C::x, but in our
experience, users have had more difficulty in distinguishing
that C::x does NOT mean "the only x in the type C" but rather
that it means "the x in the type created by a default
specialization of C".  This tends to be less an issue
when using C explicitly in a type construction context.

The grammar actually requires a "class_identifier" as the
prefix of "::".  I think there is a distinction in that
allowing "C::x" confuses the idea of "class type" and
"parameterized class as a type constructor".

Our basic approach so far has been to allow a
default specialization only in a context in which an explicit
specialization would be permitted.  Since the current
BNF doesn't allow C#(1)::x, we don't allow C::x.  Since
the BNF does allow any of:
    typedef C#(1) C_1_type;
    C#(1) some_obj;
    class D extends C#(1); .... endclass;
(and a few others), we allow default specialization in those
contexts.

This was an LRM interpretation judgement call; I would
certainly be in favor of a clarification here.

If we would allow explicit specialization in any of
the other contexts, I'd be more amenable to allowing
implicit specialization as well even though I think that
allowing it can be quite confusing.

Gord.


Arturo Salz wrote:

> Gord,
> 
> I agree with most of what you wrote. But, I disagree with your last
> statement:
> 
> Given the declaration:
> 
>     class C #(int p = 1);
>        static int x = p;
>     endclass
> 
> Then C::x does indeed mean "the x in the type created by the default
> specialization". Otherwise, what's the point of providing a default
> parameter? 
> Why would you allow 
> 	typedef C xyz;	// this does mean the default specialization
> But not allow C::x ? 
> BTW, what about the form "C()::x"? That is very clear that it means the
> default specialization.
> 
> Another question regarding this is:
> 
>     class D #(int p = 1);
>        enum Bool { FALSE, TRUE = p };
>     endclass
> 
> Would you disallow "D::Bool" , but allow "typedef X D::Bool" ?
> 
> I would agree with your assessment if Brad's proposal to omit default
> types passes and the parameterized class were written with no default.
> 
> 	Arturo
> 
-- 
--------------------------------------------------------------------
Gordon Vreugdenhil                                503-685-0808
Model Technology (Mentor Graphics)                gordonv@model.com