From: ara.t.howard@...
Date: 2006-08-02T07:02:23+09:00
Subject: Re: Strategies for autoloading ruby files

On Wed, 2 Aug 2006, Luke Kanies wrote:

> 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

this may be helpful (or not!  ;-))

   http://codeforpeople.com/lib/ruby/dynaload/

i use it for plugins in my satellite processing system like so


   class PlugIn
     def self.inherited other
       Dynaload::export self, 'plugin' => true
     end
   end


then plugins are written something like


   require 'plugin'

   class MyPlugIn < Plugin
     #
     # stuff
     #
   end


then, assume that is saved in myplugin.rb, then i can do


   require 'dynaload'

   loaded = Dynaload::dynaload 'myplugin.rb'

   plugins = loaded.select{|klass, attributes| attributes['plugin'] == true}


make sense?

the reason it's at 0.0.0 is that it just worked for me - been using in
production for a long time.

cheers.

-a
-- 
we can never obtain peace in the outer world until we make peace with
ourselves.
- h.h. the 14th dali lama