RE: [sv-ec] base interface class references (Mantis 1356)

Access to a static property of a class from a variable with the . operator is equivalent to accessing that member from the variable's type with the :: operator with an additional check that the variable is not null. That check for null would explain why this statement is in 8.5:

"Such an expression is not a constant expression."

Consider the following:

class vector #(parameter width = 7);
endclass

class array #(parameter width = 5, height = 7) extends vector #(height);
endclass

initial begin
  array #(5, 3) a = new;
  vector #(3) v = a
  $display (v.width);
end

Class properties are never treated as virtual, so v.width will refer to vector#(3)::width, and not array#(5,3)::width. From that perspective, in your second example, der.p would be equivalent to derived::p which is invalid since derived doesn't have a member p, but b.p would be legal because that is equivalent to base#(3)::p.

Do you think that language needs to be added somewhere to clarify that? What do you want to add and where?

-Brandon

-----Original Message-----
From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of Gordon Vreugdenhil
Sent: Tuesday, June 07, 2011 8:36 AM
To: SV_EC List
Subject: [sv-ec] base interface class references (Mantis 1356)

Consider the following:

     class base#(parameter p = 1);
     endclass

     class derived extends base#(3);
     endclass

Assume I then have something like:
     derived der = new;
     base #(3) b = der;

Per 8.5, it is legal for me to reference "der.p".

Will the same thing be legal for a interface class?

     interface class base#(parameter p = 1);
     endclass

     class derived implements base#(3);
     endclass

     derived der = new;
     base #(3) b = der;

Is "b.p" a legal reference here? "derived" definitely
does not inherit (or implement) the parameter "p".
Conceptually, "p" is not part of derived at all, so is it
legal to reference it via a base interface class variable
whose handle is an implementing class? If "b.p" is
legal, is "der.p" legal?

Gord.

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