RE: [sv-ec] virtual methods issues - disable on virtual, virtual method with static life time

This answer rises lots of other similar issue
1. most important: Where does LRM states that:
"Hierarchical references cannot be started with class handles. "

2. What about implicit handles (this)
class A;
	task t1;
	endtask

	task t; 
		disable t1;	// this is same as : disable this.t1 - is it
legal???
	endtask
endclass 

3.What about <BASE_CLASS? References:
Class B; task t; endtask endclass
Class C extends B; task t; disable B::t; endtask

DANiel
-----Original Message-----
From: Steven Sharp [mailto:sharp@cadence.com] 
Sent: Tuesday, May 27, 2008 10:06 PM
To: sv-ec@eda.org; daniel.mlynek@aldec.com
Subject: Re: [sv-ec] virtual methods issues - disable on virtual, virtual
method with static life time


>From: "Daniel Mlynek" <daniel.mlynek@aldec.com>

>Below code presents two issues of virtual methods - LRM does not define 
>how it they should work . Description in comments
> 
>class B;
>     virtual task static   t(input i, output o);
>        int y;
>        o = i;
>    endtask
>endclass
> 
>class A extends B;
>     virtual  task static  t(input i, output o);
>        int y;
>        o = 2*i;
>    endtask
>endclass
> 
>module top;
>        B b;A a=new;
>        initial  begin
>            b=a;
>            disable b.t; //which method would be disabled, does disable 
>take polimorphism into account?
>            b.t.i=10; //which method port would be assigned - does such 
>assignment take polimorphism into account? ()
>            b.t.y=10; //which method port would be assigned - does such 
>assignment take polimorphism into account? ()
>        end
>endmodule


I think the answer is that none of these 3 lines of code is legal, so the
question does not arise.

The later two are attempts to do hierarchical references to variables in a
scope.  Hierarchical references cannot be started with class handles.  They
must start with static hierarchy: an instance, block name or class scope.
You cannot refer to b.t.i; you must refer to B::t.i or A::t.i.  Since you
cannot use a class handle, the issue of polymorphism does not arise.  You
must use a static class scope, which specifies exactly which task you are
referring to.

The disable statement also takes a hierarchical reference, to a scope.
So again, it cannot start with a class handle.  It must start with static
hierarchy.  You would have to use B::t or A::t instead.

Steven Sharp
sharp@cadence.com


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