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Subject: Re: Objects of objects (was Re: [geda-user] The state of gEDA/gaf (Was gEDA/PCBs diversity, Was: Pin hole size))
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From: John Doty <jpd AT noqsi DOT com>
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Date: Wed, 31 Oct 2012 10:44:41 -0600
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To: Karl Hammar <karl AT aspodata DOT se>
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On Oct 31, 2012, at 3:07 AM, Karl Hammar wrote:

> John Doty:
>> On Oct 29, 2012, at 2:53 PM, Dave McGuire wrote:
>>> On 10/29/2012 04:38 PM, John Doty wrote:
> ...
> [about pcb]
>>>> To me, the conceptual mess remains. As I said, it's like driving
>>>> through downtown Boston: it's all random special cases, no
>>>> structure.
>>> I dunno.  The boards I make with it work just fine.  Why do I never
>>> run into these limitations, when I use PCB very frequently, while you, a
>>> person who just said they don't lay out their own boards, see all of
>>> these horrible problems?
>> 
>> I can't grok all the magic properties of its peculiar set of
>> abstractions. "Polygon" doesn't mean a geometric object and
>> "elements" are not elementary.
> 
>> The idea that objects are composed of objects composed of objects, ... is missing.
> ...
> 
> This kind of recursion is missing from gschem also, or rather from
> the sch/sym file formats.

It's potentially there in the format, in several flavors, actually.

1. An embedded symbol is a composite object (but gschem can't edit it, which is an annoying restriction).

2. The format allows you to attach any collection of objects to any object. The tools don't, however, support this except for attributes (and the attachment must be flat, although the format uses {}, making this potentially nestable).

> 
> You can get it - sort of - by special casing a symbol with a
> source attribute.

That's another way. I don't know why you call this "special casing": I consider this a perfectly normal use of a symbol (usually a custom symbol representing the subcircuit). I do this very frequently.

> 
> The above kind of recursion would be nice to have, are people positive
> to a discussion that would lead to an implementation of it ?

I know Peter Brett is hostile to allowing the file format to be used in generalized ways: he wants to have semantic restrictions in libgeda. But as a user of the unappreciated flexibility in the format (see, for example, pins2gsch at http://www.gedasymbols.org/user/john_doty/tools/ once DJ gets back on line), I oppose this.

John Doty              Noqsi Aerospace, Ltd.
http://www.noqsi.com/
jpd AT noqsi DOT com