From: Sean O'Dell <sean@...>
Date: 2004-06-25T08:14:53+09:00
Subject: Re: rubygems thoughts

On Thursday 24 June 2004 15:29, Gavin Sinclair wrote:
> On Friday, June 25, 2004, 8:07:45 AM, Sean wrote:
> > On Thursday 24 June 2004 14:01, Jim Weirich wrote:
> >> Sean O'Dell said:
> >> > Use YAML as the control file instead of native Ruby.  I think it would
> >> > make automating builds easier.  Ruby is okay when you're
> >> > hand-crafting, but it makes automated build creation a little dicey. 
> >> > Not terribly, but a little.
> >>
> >> Actually, the .gemspec file is optional, and I never build one for my
> >> projects.  I just use Rake to control the building of the
> >> Gem::Specification object directly and then generate the gem from the
> >> spec object.  Details can be found here:
> >> http://rubygems.rubyforge.org/wiki/wiki.pl?CreateAGemUsingRake
> >>
> >> If you want to build the spec automatically, but don't want to use Rake
> >> (shame on you), just create the Gem::Specification object in your code
> >> (as you would in a gemspec file).  To create the gem from the
> >> Gem::Spcification, just use:
> >>
> >>    builder = Gem::Builder.new(spec).build
> >>
> >> If you want a yaml file out of the process, build the spec and write out
> >> the results of spec.to_yaml.
> >
> > That sounds like what I need.  Can I re-constitute the YAML into a native
> > Ruby data structure and pass it to Gem::Builder.new?
>
> I'm sure you can, but I reckon this sounds like the more difficult way
> to do things.  I don't see why building a gem requires run-time
> generation of its specification, beyond the package version.  It
> should all be known upfront.

I agree, but I don't mind having to call a little code to load my own YAML and 
create the final .gem.  If Gems had the ability to build directly from a YAML 
config file, that would be nice, but it's good enough for me being able to 
call Gem::Builder.new(spec) where spec is a data structure I just loaded from 
YAML.  It's only 2 calls, and I'd make them from my build-generating script 
anyway, so I don't mind.

> What actual difficulty or restriction does a normal .gemspec (or
> better yet, a Rakefile gme package task) cause you?

It's native Ruby code, and since I generate the .gemspec file with code, I'd 
prefer I was generating something with more "rules" like YAML, and that I 
could use the result elsewhere (like merging spec data into a web page or 
whatever).

> BTW you asked somewhere about seeing detailed information about a gem.
> If you have a gem X installed, then try this:
>
>   gem --info X
>
> It will print out the spec in YAML.

That works pretty much, if I can call that on any .gem file.  I was thinking 
not so much of using the YAML data for human-reading as much as automatically 
pumping into other things, like web pages, or a database or whatever.

> > I'd prefer that .gemspec was just static meta data and contained no
> > code.  But as I understand it, the .gemspec file is used to create a
> > static data structure that Gem::Builder uses, so maybe that point is
> > moot.  I think I can load a static YAML file that I generate myself
> > and pass it to Gem::Builder.new.
>
> I'll be interested to see how this goes.  I'd be even more interested
> to see if there's a reason that YAML generation is better for you.
> Whether there is or there isn't, either way there's an opportunity to
> document some best practices out of this.

Well, two places it would be useful.  One, if the YAML file could be extracted 
from the .gem file (which I think gem --info X does) then you can merge the 
information into web pages and such (think of a richer gem download web page 
at Rubyforge).  Third-party version systems would be possible, etc.  The 
other is, pre-build-time.  As a developer, say I take my .gemspec file which 
is normally used only by Gems and I ssh it up to a web site somewhere, which 
dynamically merges the information in the .gemspec with a web page to show 
everyone visiting the current version, the dependencies and so on.  You could 
even generate a script that loads the YAML and contacts RAA and updates your 
RAA entry with all the latest information.

Also, and this is a little mystic perhaps, I find that simply using YAML 
whenever I can opens doors to doing other things I don't initially imagine.

	Sean O'Dell