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List:       gentoo-dev
Subject:    Re: [gentoo-dev] What are || ( ) dependencies?
From:       Ciaran McCreesh <ciaran.mccreesh () googlemail ! com>
Date:       2010-12-19 13:51:10
Message-ID: 20101219135110.2b389cd4 () snowcone
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On Sat, 18 Dec 2010 22:22:07 -0800
Zac Medico <zmedico@gentoo.org> wrote:
> >> What about if you decide upon a early on, and then later on
> >> something hard-depends upon b?
> > 
> > Then you're collapsing the graph too early. =)
> > (speaking as an utter novice)
> 
> This is the same kind of case as in bug 264434. We solved it in
> portage by putting || and virtual dependencies on stack, and delaying
> their evaluation until as late as possible. You may be able to dream
> up some corner cases where this approach doesn't help, but in
> practice it seems to help more often than not.

That's just another case where a fancy heuristic sometimes gives you
better results, but in general doesn't solve the problem at all. If
you've got two lots of undecided || ( ) deps, sooner or later you have
to decide at least one lot, but you can't correctly make that decision
until you've decided the other lot (which of course then can't be
decided until you've decided the first...).

We're all having to be way too clever here, and it isn't even helping.

-- 
Ciaran McCreesh

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