RE: [sv-ec] Re: [sv-bc] explicit package exports

I'm reassured when I hear that a feature "does not exist in any other
language", because I'm probably headed in the right new direction.

VHDL is a great language, but there's always room for improvement

     http://www.accellera.org/activities/vhdl/

-- Brad

-----Original Message-----
From: Rich, Dave [mailto:Dave_Rich@mentor.com] 
Sent: Friday, September 15, 2006 9:47 AM
To: Brad Pierce; sv-bc@eda-stds.org; SV_EC List; sv-ac@verilog.org
Subject: RE: [sv-ec] Re: [sv-bc] explicit package exports

Brad,

19.2.1 "The import statement provides direct visibility of identifiers
within packages. It allows identifiers declared within packages to be
visible within the *current* scope without a package name qualifier."

Current scope means any statement that is a member of that scope has
visibility to that import, and not to scopes that are not members of
that scope.

Given that this use model has been proven with VHDL, and chaining of
package imports does not exist in any other language, I don't see why
one would think that chaining of import is required to be useful.

The agreement that we reached in the committee meeting on Monday was
that to get consensus, we would have the default import not do chaining
as long as we could define an a way for the users to change the default
behavior. That is how we came up with the export idea.

Dave




> -----Original Message-----
> From: owner-sv-bc@server.eda.org [mailto:owner-sv-bc@server.eda.org]
On
> Behalf Of Brad Pierce
> Sent: Friday, September 15, 2006 8:31 AM
> To: sv-bc@server.eda-stds.org; SV_EC List; sv-ac@server.verilog.org
> Subject: Re: [sv-ec] Re: [sv-bc] explicit package exports
> 
> Shalom,
> 
> Package chaining seems the obvious thing when you have a mental model
of
> a package reference as being like a link in a file system.  In a file 
> system, the entire chain of links behind the simple local name is 
> automatically followed by the OS until hitting the actual file. (This 
> same mental model makes aliasing a natural idea.)
> 
> If there were really any LRM examples that "clearly imply that import 
> chaining was not intended", then testing with the LRM examples would 
> have revealed a mismatch between the intent and what seems obvious
under
> the file system analogy.
> 
> What's most important, of course, is that the SV package mechanism be
as
> usable as possible.
> 
> -- Brad
> 
> -----Original Message-----
> From: owner-sv-ec@eda.org [mailto:owner-sv-ec@eda.org] On Behalf Of 
> Bresticker, Shalom
> Sent: Friday, September 15, 2006 4:26 AM
> To: Gordon Vreugdenhil
> Cc: sv-bc@eda-stds.org; SV_EC List; sv-ac@verilog.org
> Subject: RE: [sv-ec] Re: [sv-bc] explicit package exports
> 
> 'local import' could be useful together with 'export *::*' as a way to

> say, 'export everything except a particular imported item'.
> 
> A separate question: since wildcard exports as proposed would only 
> export items actually imported and not import candidates, how could I 
> export all of p1 to p3 via p2? I would think that could be useful.
> 
> Finally, when I read 19.2 in 1800-2005, I think the language and the 
> examples clearly imply that import chaining was not intended. Possibly

> nobody even thought about it till now. Other interpretations of the
text
> are basically based on the argument that the text does not explicitly 
> say it does not happen. I don't accept that argument. In my opinion,
the
> total lack of reference to it means the reverse.
> 
> Shalom
> 
> > -----Original Message-----
> > From: owner-sv-ec@server.eda.org [mailto:owner-sv-ec@server.eda.org]
> On
> > Behalf Of Gordon Vreugdenhil
> > Sent: Friday, September 15, 2006 12:46 AM
> > To: Greg Jaxon
> > Cc: Brad Pierce; sv-bc@server.eda-stds.org; SV_EC List; sv- 
> > ac@server.verilog.org
> > Subject: [sv-ec] Re: [sv-bc] explicit package exports
> >
> >
> >
> > Greg Jaxon wrote:
> >
> > > Well  "local import Q::myInt;"  seems odd if the default will be 
> > > local visibility for imports.  Also "local export Q::myInt;" seems

> > > self-contradictory.
> >
> > I don't think that "local import" is very useful and would be fine 
> > with making it illegal.  In any case, the exact rules for
interactions
> 
> > between "local" and "export" are certainly subject to a debate that 
> > I'd rather leave as a separate question.
> >
> > "local export" would not be valid -- "export" is not a 
> > package_or_generate_item_declaration in my proposal, it is a 
> > "package_item" itself so my suggested BNF change wouldn't apply to
the
> 
> > package_export_declaration rule.
> >
> > Gord.
> >
> >
> > >
> > > Greg
> > >
> > > P.S. To me this argues for default public visibility (i.e. import
==
> 
> > > export),
> > >      but as I understand it the committees hav already reached a
> > compromise
> > >      to not do that.
> > >
> > > Gordon Vreugdenhil wrote:
> > >
> > >>
> > >>
> > >> Brad Pierce wrote:
> > >>
> > >>> The first option is the right way to go and doesn't look ugly to
> me.
> > >>
> > >>
> > >>
> > >> I should have been more careful in how I phrase that -- the first
> > option
> > >> isn't ugly but I don't want to have to dig through all the
semantic
> 
> > >> implications on my own.  The second option would be ugly.
> > >>
> > >> Does anyone have opinions on when "local" should NOT be permitted
> for
> > >> the proposed change:
> > >>     [ local ] package_or_generate_item_declaration
> > >>
> > >> "local" might not make sense to me in the context of things that
> > might
> > >> not have names but I'm not sure if that can happen here given
other
> 
> > >> semantic constraints.
> > >>
> > >> Gord.
> > >>
> > >>> -----Original Message-----
> > >>> From: Gordon Vreugdenhil [mailto:gordonv@model.com] Stuart 
> > >>> Sutherland wrote:
> > >>>
> > >>>
> > >>>> I agree that adding 'local' to package declarations is
intuitive
> > and
> > >>>> makes for self-documenting code.  Since it is likely that it
will
> > be
> > >>>> the intent that most package items will be visible to importers
> of
> > the
> > >>>
> > >>>
> > >>>
> > >>>> package, only a few, if any, items will typically need to be 
> > >>>> declared as local.  If, on the other hand, the export was used
to
> 
> > >>>> make package items "importable" (a new word?), then to hide a
> small
> > >>>> number of items
> > >>>
> > >>>
> > >>>
> > >>>> would require explicitly exporting almost all other package
> items.
> > >>>>
> > >>>> I also think it makes sense to include local package items as
> part
> > >>>> of the export proposal.  The two go hand in hand.
> > >>>
> > >>>
> > >>>
> > >>>
> > >>> The grammar changes for allowing "local" to package declarations
> > might
> > >>> be a bit ugly.  There are two choices -- the easy choice is to
add
> 
> > >>> "local" as an optional qualifier in the package_item rule.  Ie:
> > >>>
> > >>>     package_item ::=
> > >>>          [ local ] package_or_generate_item_declaration
> > >>>        | anonymous_program
> > >>>        | timeunits_declaration
> > >>>
> > >>> Then we might have to have some semantic constraints that
"local"
> > >>> isn't legal for some constructs but I'm not sure if that is in
> fact
> > the
> > >>> case.
> > >>>
> > >>> The other option would be separate
> > package_or_generate_item_declaration
> > >>> into two parts -- one for packages and the other for generates.
> > >>>
> > >>> I am willing to add the former solution and a bit of text to
what
> I
> > am
> > >>> writing up but I don't want this to snowball and I don't have
the
> > time
> > >>> to try to figure out all of situations in which "local" on a 
> > >>> package_or_generate_item_declaration might not be reasonable.
If
> > people
> > >>> are Ok with the simple change, fine, otherwise let's separate
> > "local"
> > >>> from export so that there can be more time for consideration.
> > >>>
> > >>> 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
>