RE: [sv-ec] Prohibit overriding data members of a class?

Jonathan,

Evidently, the simulator used by the student has a bug. He should see
"3" and "4", as expected.

BTW, only virtual methods truly override methods in base classes. All
other methods and properties do not override but provide name hiding.
Hence, in your example, class D has two properties called "N" and two
methods called "get_N", one in class D proper and one in its super class
(class C), each one is accessible via an object handle of the
corresponding type. Only from the perspective of class D is the property
overridden. If you had declared a virtual method Boo in class C and in
class D then an object of type D would have only one method
implementation - that of class D, regardless of the object pointer used.

  class C;
    int N = 3;
    function int get_N(); return N; endfunction
    virtual function int Boo(); return 5; endfunction
  endclass
  class D extends C;
    int N = 4;
    function int get_N(); return N; endfunction
    function int get_N1(); return super.N; endfunction
    virtual function int Boo(); return 6; endfunction
   endclass
  ...
  ...
  D d = new;
  C c = d;		// Note same object!
  $display(c.get_N());  // "3"
  $display(d.get_N());  // "4"
  $display(d.get_N1()); // "3"  - super.N
  $display(c.Boo());    // "6"
  $display(d.Boo());    // "6"
  c = new;
  $display(c.Boo());    // "5"

	Arturo

-----Original Message-----
From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
Jonathan Bromley
Sent: Friday, October 19, 2007 7:15 AM
To: sv-ec@eda.org
Subject: [sv-ec] Prohibit overriding data members of a class?

hi EC,

I recently had a query from a student who had tried to 
override a *data* member of a class...

  class C;
    int N = 3;
    function int get_N(); return N; endfunction
  endclass
  class D extends C;
    int N = 4;
    function int get_N(); return N; endfunction
  endclass
  ...
  ...
  D d = new;
  C c = new;
  $display(c.get_N()); // "3" as expected
  $display(d.get_N()); // "3" seen ???!!!

(By the way, I don't even know which simulator this person
was using.)

It seems to me that this should be illegal, and you should
be able to override only methods, not data members.  Although
the LRM hints as much, I can't find an explicit prohibition
of overriding a data member, nor a description of what to do
should it occur.

Any other opinions?  Is this just a compiler failing to
report an error, or have I missed something?  Do we need
some minor LRM clarification for this?
-- 
Jonathan Bromley, Consultant

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