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