RE: [sv-ec] question about name resolution in classes

 
Gordon,

That is an interesting sophisticated example where the base class is not
known until elaboration.
I agree that there are some lexical ways for removing ambiguity in which
scope to resolve a
symbol (this, super). If we follow the normal verilog name resolution rules,
in your example, since there is a child.i, i would resolve to child.i

My opinion is that if there was an import p::*, then the parser needs to
attempt to resolve
the symbol by looking up in the package. The package look up is now part of
name resolution
as I had pointed out before. 
If the user needs to specify that i is a property of the class hierarchy,
super.i needs
to be used. If the symbol is not resolved at that point (no import and no
static i), I would
think that in your case we ought to consider 'i' as an oomr which may be
resolved at
elaboration. We should only consider this last resort because type of the
immediate scope
containing the symbol 'i' is not known until elaboration and i because it is
a simple name
needs to be resolved in that scope.
That scope is not *complete* until elaboration.
This is a new case of oomrs. Usually (with the exceptions of functions and
tasks) an oomr
consists of more than 1 token separated by '.'

In summary, I expect the following:

During parsing, normal Verilog name resolution rules (augmented by
systemVerilog package look up)
apply, 
then if the symbol is still undefined and the scope in which it appears is a
type which is
not known until elaboration, then the symbol is an oomr which is resolved at
elaboration when the type
is known.

Another approach is to avoid the oomr for simple name and require that i be
resolved at parsing time.
However if super.i is used, allow the oomr to be resolved at elaboration.

Francoise
    '

-----Original Message-----
From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of Gordon
Vreugdenhil
Sent: Thursday, March 23, 2006 6:40 PM
To: francoise martinolle
Cc: sv-ec@eda.org
Subject: Re: [sv-ec] question about name resolution in classes

Francoise,

This is an area that is quite a bit more interesting than even your example.

The basic question is how to align lexical (and package) search rules with
class member and property lookup.

In the package case (such as yours), since the package is required to exist,
the resolution of the base type is required to be known, so I think the
intuitive answer is that "i" is the member reference and needs to be
resolved as such.  It isn't clear to me however that this is going  to end
up being the answer.

There are other contexts which are far more difficult since there are
separate compilation issues that come into play.

Consider:

    module child;
       parameter type T = int;

       int i;
       class derived extends T;
           function void dump;
               $display(i);
           endfunction
       endclass
    endmodule

    package p;
       class base;
           bit b;
       endclass
    endpackage

    module top;
       class base;
          int i;
       endclas

       child #(base) c1();
       child #(p::base) c2();
    endmodule

In this scenario, what does "i" mean in class derived?  You can't possibly
know what it is or whether it is even lexically resolved to child.i or
resolved in the context of the class hierarchy.
In my example, the answer changes in the different module instances.

Since module child is a valid module for separate compilation there is no
way to determine the answer at compilation; elaboration time is the earliest
at which this can be resolved.

This is complicated by the package import rules.
If you didn't have "i" declared in "child" but it was potentially visible,
would you do the import and make it actually visible?

One reasonable approach to the general problem is to require a "this." or
"super." prefix for references to inherited members in at least some
situations.

I don't think there is any ideal solution to the naming issue since you
either have to deal with syntax requirements or have to try to define some
reasonable rules for when an implementation is required to know things about
the inheritance structure and when the user is required to disambiguate.

This is loosely related to the issues with randomize() that Ray and I have
been working on a proposal to address.

Gord.


francoise martinolle wrote:
> Supposed I have a base class in a package and I create a derived class 
> of that class in a module. I do not import the package but I use the 
> package scope syntax to indicate the base class. Does this cause all 
> the class item declaration of the BASE class to be visible in the 
> derived class?
>  
> I think it should.
>  
>  
> package p;
> class BASE;
>   rand logic i;
> endclass
> endpackage
>  
>  
> module top;
> class derived extends p::BASE;
>        constraint c1 { i == 1'b1};
> endclass
> endmodule
>  

--
--------------------------------------------------------------------
Gordon Vreugdenhil                                503-685-0808
Model Technology (Mentor Graphics)                gordonv@model.com