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Subject:	Re: [geda-user] Difference between attached and detached attributes
From:	John Doty <jpd AT noqsi DOT com>
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Date:	Sat, 18 Jul 2015 17:41:25 -0600
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On Jul 18, 2015, at 4:09 PM, Roland Lutz <rlutz AT hedmen DOT org> wrote:

> You can delete an inherited attribute by
> attaching an attribute with the value "unknown" to the component.

That depends a bit on the gnetlist back end. The primitive gnetlist:get-all-package-attributes yields #f (Scheme’s token for falsehood) for a missing attribute. The derived gnetlist:get-package-attribute substitutes “unknown” for this. Back ends generally use gnetlist:get-package-attribute and interpret “unknown” as the token for a missing attribute. That is not, however, required behavior. 

Things get more interesting if you have multiple symbols for one refdes. The default behavior is difficult to predict (that’s what I call the “attribute censorship bug”). If you’re using my censor-fix.scm, a missing attribute does not conflict with an attribute associated with a different symbol, but an attribute of “unknown” will conflict unless all symbols agree that it’s “unknown".

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

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