From: Luke Kanies <luke@...>
Date: 2006-08-02T06:53:36+09:00
Subject: Strategies for autoloading ruby files

Hi all,

Following up on my post about complicated problems, here's a much 
simpler problem that I need to tackle.

There are many parts of my framework that are extensible, and I want 
people to be able to create extensions without modifying the core 
framework, akin to how you don't have to specifically load each model 
and controller in Rails.

Is there a relatively standard way of doing that with Ruby?  This is 
what I'm doing in one of my projects, Facter[1]:

         # Now see if we can find any other facts
         $:.each do |dir|
             fdir = File.join(dir, "facter")
             if FileTest.exists?(fdir) and FileTest.directory?(fdir)
                 Dir.glob("#{fdir}/*.rb").each do |file|
                     # Load here, rather than require, because otherwise
                     # the facts won't get reloaded if someone calls
                     # "loadfacts".  Really only important in testing,
                     # but, well, it's important in testing.
                     begin
                         load file
                     rescue => detail
                         warn "Could not load %s: %s" %
                             [file, detail]
                     end
                 end
             end
         end

I've tried further copying Rails by checking that loaded files create 
the objects it seems they should create (e.g., here they should create a 
fact named after the file), but users constantly complained about those 
warnings.

Is this the best way?  Any other recommended mechanisms?

I'd actually like the autoloading to work either on-demand (e.g., look 
for 'facter/myfact' if I ask for the 'myfact' fact), or load all of them 
right now.

Hmm.  In fact, it'd be ideal if you could write a module that allows you 
to register autoload paths (e.g., I'd use 'facter', 'puppet/type', 
'puppet/type/package', 'puppet/type/service', and lots more), and then 
just have hooks into that module so that you could autoload all 
instances, or just load a specific name.

1 - http://reductivelabs.com/projects/facter

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Luke Kanies | http://reductivelabs.com | http://madstop.com