From: "Luke A. Kanies" <luke@...>
Date: 2003-12-24T05:23:55+09:00
Subject: Re: RubyGems and dependencies

On Wed, 24 Dec 2003, Joey Gibson wrote:

> On Wed, 24 Dec 2003, Francis Hwang wrote:
>
> > 1. If I use RubyGems to document a dependency to another gem then am I
> > correct in thinking it's not enough to simply have had that library
> > installed -- I explicitly need that gem, right? I mean, Lafcadio
> > depends on REXML and when I try to install the Lafcadio gem it tells
> > me it can't find the REXML gem. REXML is already installed (I'm using
> > Ruby 1.8 so it's part of the std library) but I'll need to install the
> > REXML gem so that my Lafcadio gem will work, right?
>
> This is the situation I tried to point out at RubyConf that I'd seen with
> RedHat's rpm package manager. Namely that if I've already installed a
> piece of software, without using the package manager, what will happen
> when I try to install something else that _does_ use the package manager?
> I don't really know how to solve it unless you can fake out the package
> manager (gem-thingy) or have the gem producer provide some sort of test
> that the gem-thingy can use at install time to check for the existence of
> a piece of software that was installed manually. Maybe a filename/pathname
> that it can check for as a last resort if the gem for a needed something
> isn't found.

Isn't this a relatively straightforward 'require <lib>' test?  I don't
know exactly how CPAN decides if a package is installed or not, but it has
always seemed as though it does something along the lines of:

perl -M<lib>
if [ $? != 0]; then
   echo Missing pkg <lib>
   # blah blah
fi

This is certainly an easy thing to do in ruby:

begin
   require '<lib>'
rescue <missing lib error>
   # give a warning, maybe try to install the lib, and then
   # redo this section, probably
end

Luke

-- 
    The Washington Bullets are changing their name.  The owners no
    longer want their team's name to be associated with crime.  So from
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                -- Paul Harvey, quoting Argus Hamilton