Re: FW: [sv-bc] parameterized structures

Bresticker, Shalom wrote:

> Resend for Greg
> 
> -----Original Message-----
> From: owner-sv-bc@server.eda-stds.org [mailto:owner-sv-bc@server.eda-stds.org] On Behalf Of Greg Jaxon
> Sent: Friday, June 16, 2006 10:38 PM
> To: Gordon Vreugdenhil
> Cc: sv-bc@server.verilog.org
> Subject: Re: [sv-bc] parameterized structures
> 
> Gordon Vreugdenhil wrote:
> 
> 
>>There is another important difference -- C++ doesn't have the
>>additional "elaboration" phase that Verilog has and as a result
>>essentially all "template" analysis is a compile time
>>activity. 
> 
> 
> C++'s template instantiation phase is driven by a fixed-point linking
> discipline that is essentially identical to design elaboration.  The 
> compiler is not done cranking out template instantiations until no 
> new ones are demanded and the last one is specialized.
> 
> 
>>In SV, different elaborations of a parameterized
>>class create different universes for instantiation.
> 
> 
> I don't understand the phrase "different universes for instantiation".
> Of course each parameterization of an SV class, like a C++ template class 
> specialization, produces a particular class (a new data type) which then 
> governs the behavior of a family of class instances.  That's like a 
> universe in which you can construct new instances...
> 
> 
>> There is no corresponding concept in C++.
> 
> 
> Which could be why I am not recognizing it. Are you sure that brief section 
> 7.23 is inventing something new under the sun?


The issue here is in the following desgin:

   module top;
     child c1();
     child c2();
   endmodule

   module child;
     class C #(int p = 1);
     endclass

     C #(2) c_obj;
   endmodule

The two *elaborated instances* of child produce distinct
parameterized classes where each will end up with one specialiation.
The two specializations are distinct; one is based on the parameterized
class in top.c1 and the other is based on the parameterized class
in top.c2.  Each elaboration of child creates a new universe of
specializations related to the elaboration of the new parameterized
class.

This means that top.c1.c_obj is not assignment compatible with
top.c2.c_obj.

> If you can prove that no name-mangling approach will ever work for SV, 
> then the game is up - the language is simply uncompilable.
> This might be a true statement.  


I said that no *static pre-elaboration* name mangling can work.  In other
words, it is not possible to independently compile "child" and create a
fixed universe of types since each elaboration time instantiation
of "child" creates additional types that are required to be distinct.

Clearly all of this is compilable (existence proofs exist), it is
just a bit more dynamic than one might think.

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