Re: [sv-ec] "this" and member resolution in inline constraints

Mark Hartoog wrote:
> I am confused by what the issue is here.

It is clarity of the text for the non-implementor.

> Compile time resolution is always in terms of the statically declared 
> fields and methods. Some methods may be declared virtual in the static
> class. 
 > This means that at compile time you resolve to the virtual
> method.
> All type checking is done against the virtual method. The actual method
> that is called is selected at run time. Data field members are never
> virtual. 
> 
> In your example the 'x' in the randomize with block resolves to the int
> 'x' in 
> class 'C'. 


Sure, you and I and other implementors know that.  I'm certainly
not suggesting any other binding.


What the text doesn't say is:
   1) that the inline constraint is effectively its own non-virtual
      method rather than being "part of" randomize.  Without
      such a statement the only "this" that a reader could assume is
      the "this" of the randomize method that is *actually called*.
      That type is not known.
   2) that the class in which the "method" lives is the class
      defined by the type of the reference

The current approved 1858 text talks about "the randomize...with object"
and NOT the type of the reference.  That could easily lead readers
to assume the highly dynamic behavior.

By the way, you certainly cannot tell the type of the class reference
at compile time -- if the prefix is a general hierarchical reference
or similar then you can't possibly know until elaboration time.  So
where the names bind is certainly an elaboration time decision
based on the static type of the reference; the non-virtual method
model is just a convenient way to talk about the effect.

Gord.


> 
> 
> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of
> Gordon Vreugdenhil
> Sent: Tuesday, December 18, 2007 1:50 PM
> To: SV_EC List
> Subject: [sv-ec] "this" and member resolution in inline constraints
> 
> 
> In considering some of the wording for the 1858 (inline constraints name
> resolution) issues, I would like to raise an additional concern and/or
> need for clarification.
> 
> "randomize" is definitely a virtual method.  In the discussion, we were
> talking about "this" as following the normal method resolution rules for
> "this" references.  That does pose a problem when everything is
> composed.
> 
> Consider this case:
> 
>            class C;
>               rand int x;
>            endclass
>            class D extends C;
>               rand bit[1:0] x;
>            endclass
>            D d = new;
>            C c = d;
> 
>            initial c.randomize with { x > 0 && x < 10; };
> 
> My working assumption has always been that the resolution of "x" is
> based on the static type of the object prefix, but I think that the
> wording and discussion related to "this" has at least muddied the waters
> if not compromised that interpretation completely.
> 
> If I have:
>           initial c.randomize with { this.x > 0 && this.x < 10; }; the
> meaning of "this" is now different.  We would have to interpret "this"
> not as the formal of the virtual method "randomize"
> but as "a reference to the portion of the object addressable by the
> static type of c".
> 
> There are many, many issues with a dynamic interpretation of "this" so I
> would not want to propose that we follow the dynamic resolution path.  I
> believe that the statically typed interpretation I have above is
> consistent with Arturo's view.
> 
> Since "this" would not follow the normal semantics of a virtual method,
> I think that this needs to be reexamined or clarified as part of 1858.
> 
> If the more static view of name binding is followed, there are still
> potential questions related to handling of other virtual method
> references within a constraint and the overall coherency of object
> assumptions in such cases.
> 
> Gord.
> --
> --------------------------------------------------------------------
> Gordon Vreugdenhil                                503-685-0808
> Model Technology (Mentor Graphics)                gordonv@model.com
> 
> 

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


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