From: ptkwt@... (Phil Tomson)
Date: 2003-12-24T13:36:55+09:00
Subject: Re: RubyGems and dependencies

In article <Pine.LNX.4.44.0312231138440.27882-100000@www.pocketdeveloper.com>,
Joey Gibson  <joey@joeygibson.com> 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.

Something like:

#let's see if they've already got rexml:
begin
  require 'rexml'
rescue MissingPackage #or whatever it's really called
  #it's really not here, so go look for one to download
  ...
else
  #it is here already, maybe check out the version somehow
  #otherwise everything should be OK
end

Phil