From: "Berger, Daniel" <Daniel.Berger@...>
Date: 2005-10-11T22:07:31+09:00
Subject: Re: gems is a language change, not a pkging system

> -----Original Message-----
> From: Jim Weirich [mailto:jim@weirichhouse.org] 
> Sent: Tuesday, October 11, 2005 6:36 AM
> To: ruby-core@ruby-lang.org
> Subject: Re: gems is a language change, not a pkging system
> 
> 
> 
> Berger, Daniel said:
> > I guess I'll wait to ask at RubyConf why it couldn't just scan down 
> > the sitelibdir. :)
> 
> How can you tell from sitedir whether a particular version of 
> a library has been installed?

My preference would be that gems abort if the package is found *at all*
in the sitelibdir, unless a "force" option is used.

However, you could also make a best guess:

# Or something along these lines
if File.exists?("sitelibdir/some/package")
   require "some/package"

   constants = Some::Package.constants

   if constants.include?("VERSION")
      version = Some::Package.const_get("VERSION") # classes
   else if constants.include?("PACKAGE_VERSION")
      version = Some::Package.const_get("PACKAGE_VERSION") # modules
   else
      # not found
   end
end

This would rely on a convention of people defining a VERSION constant
for classes, or a MODULE_VERSION for modules in their packages.  It's
not guaranteed to work, I realize, but it's better than nothing IMHO.

Regards,

Dan