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On 4 July 2012 05:56, Ciaran McCreesh <ciaran.mccreesh@××××××××××.com> wrote: |
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> |
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> But whether or not a and b can be installed together sounds an awful |
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> lot like a property of a and b, not of c. |
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Its just when C is really something abstract, ( a virtual ) provided |
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by both possibly a & b, and b doesn't know a even exists till after |
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the fact, and vice versa, that solving the problem in a & b becomes |
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messy. |
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|
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If you solve it in one side ( in my example, perl-core ) you end up |
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having a lot of weird conditional logic trying to work out src_uri, |
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dependencies, and whether or not to actually do anything. |
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If you solve it on the other side ( in my example, dev-lang/perl ) , |
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you end up having perl specify what versions of the abstract notion |
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can and cannot be installed, instead of the abstract notion specifying |
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what is *needed* and there is a resolution required to provide that. |
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if a package specifies : " =virtual-Foo-5.0 " , that means "I want the |
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Foo.pm version 5.0, I don't care how you get it, get it". |
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Only the virtual can convey *how* to get that. |
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ie: perhaps =virtual-Foo-5.0 can only be satisfied by installing |
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dev-lang/perl-5.10 ( its not in any other Perl, or on CPAN ) |
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or perhaps =virtual-Foo-5.0 can be satisfied by installing |
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perl-core/Foo-5.0 on any perl |
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And there are dozens of packages that ask for "Foo-5.0" , and the only |
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other altnative we had before we had the virtual/perl-* family, was to |
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ignore the dependency entirely and hope for the best, or depend on a |
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minimum perl we know had it ( which is a different minimum perl than |
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what upstream specifies, because upstream assume you can install |
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things from CPAN , and/or depend on the nearest match that *is* |
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available via perl-core/* , risking the possibility that it will |
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install a version from CPAN that is to become outdated by a future |
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perl release, but you'll keep installed anyway, giving the shadow |
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effect again. |
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Essentially, the problem at the bottom of this, is Perl Modules depend |
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on each other by components in distributions ( the modules ), not the |
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distributions themselves. Its merely convention that distributions |
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have a name and version that is the same of a module also contained in |
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that distribution. |
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|
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-- |
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Kent |
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|
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perl -e "print substr( \"edrgmaM SPA NOcomil.ic\\@tfrken\", \$_ * 3, |
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3 ) for ( 9,8,0,7,1,6,5,4,3,2 );" |
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|
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http://kent-fredric.fox.geek.nz |
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