RE: [sv-bc] Re: Package export proposal

Hi Gord,

I agree that it is cleaner to have users to do an 
"import" explicitly rather than interpreting this action
from an export statement. 

For package chaining we would need export *::*;  Although
Greg is not proposing an implied import for *::* it may
become confusing to the users, 
if there is an implied import semantics specified in the
LRM. 

Thanks

Logie. 

-----Original Message-----
From: owner-sv-bc@eda.org [mailto:owner-sv-bc@eda.org] On Behalf Of
Gordon Vreugdenhil
Sent: Friday, September 15, 2006 7:00 AM
To: Greg Jaxon
Cc: SV_BC List
Subject: Re: [sv-bc] Re: Package export proposal



Greg Jaxon wrote:

> Gordon,
> 
>    Can you clarify one aspect of this design that differs from
> my first guess as to how "export" would work?  I imagined that
> export would be identical to "import" with the only difference
> being the visibility of items which it addressed.
> 
>    But reading the proposal, I get the impression that
> 
> package Pn;
>    export Pn_1::x;
> endpackage;
> 
> would /not/ import Pn_1::x and then re-export it.
> 
> I can't think of any good reason to give an error for this case,
> and I think having export implicitly import takes some awkwardness
> out of examples such as
> 
> package p5;
>    import p4::*;
>    export p1::x;    // p1::x is visible since it is exported
>                     // from p4.
>    ...
> 
> I can sympathize that using the keyword export to also mean
> import is an unusual enlargement of its natural language meaning.


That is the main reason that I went this route.  I thought of
saying that an explicitly named export has the same effect as
an import and an export but then you get into asymmetry between
export pkg::*;  and export pkg::name;  since I don't think that
you want export pkg::*; to be an implied import pkg::*;.   Rather
than deal with that assymetry, I decided to just treat a direct
named export as a reference which then implies the behavior I
described.

I wouldn't object to going the other way if that is the consensus.
I think that it would be a bad idea to have "export pkg::*;" be
an implied import.

Gord.


> But seeing examples where every import is duplicated as an export
> reminds me of Verilog 95 port declarations, with the way they
> add one modifier at a time - not particularly succinct.
> 
> Greg
> 
> 
> Gordon Vreugdenhil wrote:
> 
>> I just caught a minor BNF bug in the proposal -- I missed the
>> vertical bar when I added the "export *::*;" rule.  I fixed
>> the typo and uploaded the modified version.
>>
>> Gord.
>>
>>
>> Gordon Vreugdenhil wrote:
>>
>>> I've uploaded an initial cut at the export proposal and
>>> attached it to Mantis 1323 as a placeholder.
>>>    http://www.verilog.org/svdb/bug_view_page.php?bug_id=0001323
>>> See the attached package_exports.htm.
>>>
>>> I think that I've managed to incorporate all the changes
>>> suggested from within the sub-group.  If anyone sees errors
>>> or omissions, please let me know.
>>>
>>> I have not yet included the "local" declaration change since
>>> I need to hear some feedback as to whether there need to
>>> be semantic restrictions on the general case.
>>>
>>> Gord.
>>
>>
> 

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