RE: [sv-ec] dynamic vars should be forbidden as defaults

I see your point and I tend to agree with you.

 

Actual arguments are not part of a method. As the pseudo-code in my
previous message shows, arguments are evaluated in the caller - before
making the method call. Hence, using "this" either explicitly or
implicitly (i.e., your f1 is essentially x=this.a) should not be
allowed. The intent of the LRM statement was to use the *static* scope
for resolution of constants. I'd be willing to add this to the LRM if
other agree.

 

            Arturo

 

________________________________

From: danielm [mailto:danielm@aldec.com.pl] 
Sent: Monday, January 21, 2008 1:07 AM
To: 'Arturo Salz'; sv-ec@eda.org
Subject: RE: [sv-ec] dynamic vars should be forbidden as defaults

 

OK - I understand yours example - it is fine for me - thanks for
explanation.

 

 

But what about my code - is it legal or not - the LRM doesn't forbid
below (case f1,f2).

 

class C;

  int a;

   static int b;

    function f1(int x=a);

   endfunction

    function f2(int y=this);

   endfunction

    function f3(int z = b);

   endfunction

endclass

 

IMHO only the 3rd (f3)should be allowed - because defaults are assigned
before the function call - so only statics are known at that moment.

 

 

 

DANiel

 

________________________________

From: Arturo Salz [mailto:Arturo.Salz@synopsys.com] 
Sent: Saturday, January 19, 2008 12:20 AM
To: danielm; sv-ec@eda.org
Subject: RE: [sv-ec] dynamic vars should be forbidden as defaults

Daniel,

 

The segment you highlighted refers only to name binding - not to
lifetime. 

 

So considering the following code: 

 

int a;

class C;

  function void f1(int x=a);

    // ...

  endfunction

endclass

 

initial begin

  bit a;

  C c1 = new;

  c1.f1();

end

 

The method call could be "conceptually" implemented as:

 

initial begin

  bit a;

C c1 = new;

int temp = $unit::a;

c1.f1( temp );

end

 

Note that the argument binds to the variable in $unit- the "a" in the
declaration - and not the "a" in the scope of the call.

That is what that statement indicates.

 

Arturo

 

________________________________

From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
danielm
Sent: Friday, January 18, 2008 7:19 AM
To: sv-ec@eda.org
Subject: [sv-ec] dynamic vars should be forbidden as defaults

 

LRM says that:  

1800-2005: 12.4.3 Default argument values:

"The default_value is an expression. The expression is evaluated in the
scope containing the subroutine

declaration each time a call using the default is made."

 

The problem arises when we use that rule for dynamic|automatic variables
- ie for class propeties:

class C;

  int a;

   static int b;

    function f1(int x=a);

   endfunction

    function f2(int y=this);

   endfunction

    function f3(int z = b);

   endfunction

endclass

 

IMHO only the 3rd (f3)should be allowed - because defaults are assigned
before the function call - so only statics are known at that moment.

 

 

Similar case may be also spotted in example with no classes:

module top;  
 task automatic t(int a = 1, int b = a); 
  $display(a,,b);
 endtask      
 
 initial t;
endmodule

 

 

In above case a is an automatic variable and doesn;'t exists at the
moment when defaults should be assigned.

 

DANiel


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