From: Brian Palmer <rubytalk@...>
Date: 2006-08-02T07:04:19+09:00
Subject: Re: Strategies for autoloading ruby files

You can use `Module.const_missing` to autoload a file the first time  
the class in that file is mentioned in the code. So you could write  
an `Object.const_missing(name)` method that translates the constant  
into a file name of an expected format, then load that file on-the-fly.

Amusingly, this is exactly the code example that's given in the  
Pickaxe version 2 under Module.const_missing, along with a note that  
the code is in very poor style and is a "perverse kind of autoload  
functionality".

:)

-- Brian

On Aug 1, 2006, at 3:53 PM, 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
>
> -- 
> The Number 1 Sign You Have Nothing to Do at Work...
>    The 4th Division of Paperclips has overrun the Pushpin Infantry
>    and General White-Out has called for a new skirmish.
> ---------------------------------------------------------------------
> Luke Kanies | http://reductivelabs.com | http://madstop.com
>
>