Re: [sv-bc] Serious issue with default expressions for task and function arguments

Gord mentions that binding different default values to different calls 
of the same function depending on the context of the call may be 
unreasonable and not in the context of separate compilation. However,
that is precisely the situation in C++. Consider the example below, which
generates the following output when run:
    foo: 2
    bar: 11
In this case, function C::F() uses different default values, depending on
the context of the call (more precisely the context of the compilation unit).
While I do agree that it may not be good coding practice, I do not believe 
it should be deemed unreasonable. Also, since C++ does allow separate 
compilation, it is definitely reasonable in that context: Proof by existence.

    Arturo

=== file C.h ===

class C {
  public:  static int F( int y = A )  { return( y + 1 ); }
};

=== file A.cpp ===

#include <stdio.h>
static const int A = 1;
#include "A.h"

void foo() { printf( "foo: %d\n", C::F() ); }

=== file B.cpp ===

#include <stdio.h>
static int A = 10;
#include "A.h"
extern void foo();

void bar() { printf( "bar: %d\n", C::F() ); }

main()
{
    foo();
    bar();
}
====

    Arturo

----- Original Message ----- 
From: "Mark Hartoog" <Mark.Hartoog@synopsys.COM>
To: <pgraham@cadence.com>; <gordonv@model.com>
Cc: <ieee1800@eda.org>; <sv-bc@eda.org>
Sent: Thursday, March 03, 2005 10:39 AM
Subject: RE: [sv-bc] Serious issue with default expressions for task and function arguments


> In this case there is no p1 visible at the point of compilation
> of function f.  Is this legal?  Is SV adopting dynamic scoping? :-)

The LRM says "The elements of the expression must be visible at the scope 
of subroutine". In your example, 'p1' would be an unresolved identifier
in the scope of the subroutine, so this would be illegal.

I think part of the confusion here is what the term "elements of the 
expression" means. When you have an expression like 'p1', I think the 
element of the expression is the object that the identifier 'p1' resolves
to in that scope. Other people seem to think that the element of
the expression is simply the identifier itself. Perhaps this needs to 
be reworded to make clear what was meant.  

> -----Original Message-----
> From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org]On Behalf Of Paul
> Graham
> Sent: Thursday, March 03, 2005 10:24 AM
> To: gordonv@model.com
> Cc: ieee1800@eda.org; sv-bc@eda.org
> Subject: Re: [sv-bc] Serious issue with default expressions for task and
> function arguments
> 
> 
> >     The default_value is an expression. The expression is evaluated in
> >     the scope of the caller each time the subroutine is called. The
> >     elements of the expression must be visible at the scope of subroutine
> 
> Here's another example:
> 
> function f(integer x = p1);
>    return x;
> endfunction
> 
> module m1(...);
>     parameter p1 = 1;
>     assign q = f(); // q == 1
> endmodule
> 
> module m1(...);
>     parameter p1 = 2;
>     assign q = f(); // q == 2
> endmodule
> 
> In this case there is no p1 visible at the point of compilation
> of function f.  Is this legal?  Is SV adopting dynamic scoping? :-)
> 
> Paul