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

Gord,

Perhaps you misunderstood the point I was trying to make.
In my example, there is only one C::F() function, *not* two 
functions a you seem to suggest. There are two invocations
(function calls) of the same function. Note that the outcome
of my example is the same if I change my code as follows:

=== file C.h ===

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

=== file C.cpp === (this is a new file)

#define A 0
#include "C.h"
int C::F( int y )  { return( y + 1 ); }

===

Now, it is very clear that only the function prototype is being
`included in each of the c files (A.cpp and B.cpp), and there
is only one C::F() function. What is different is the binding of
the default expression at each call site. This is not just lexical
binding.

    Arturo

----- Original Message ----- 
From: "Gordon Vreugdenhil" <gordonv@model.com>
To: "Arturo Salz" <Arturo.Salz@synopsys.COM>
Cc: "Mark Hartoog" <Mark.Hartoog@synopsys.COM>; <pgraham@cadence.com>; <ieee1800@eda.org>; <sv-bc@eda.org>
Sent: Thursday, March 03, 2005 11:40 AM
Subject: Re: [sv-bc] Serious issue with default expressions for task and function arguments


Arturo, you are using the equivalent of 'include to create
*different* functions in *different* contexts.

If you want to 'include a function in two different contexts
in SV, I would expect the binding as you describe as well.

Consider the following which is the same as the SV examples
that I brought up:

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

main() {
   const int A = 2;
   cout << C::F() << endl;
}


In this example, C++ will correctly bind the "A" in the default to
the one that exists in the context of F's definition.  Same thing
happens if you have:

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

main() {
 
      const int A = 2;
    cout << C::F() << endl;
}



If you 'include a function "F" into two different SV contexts,
you also get two functions with two sets of bindings.  I have
no problem with that.

Gord.



Arturo Salz wrote:

> 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
> 
> 
> 

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