model_extensions.rb

module ModelExtensions
  
  # A set of extensions to add handy can_has-style extensions for
  # classes. Based on code by Fowlduck and Faithfulgeek pasted in
  # #offrails.
  def can_has(*args)
    options = args.extract_options!
    components  = _flatten_parameters(args)
    components += _flatten_parameters(options)
    components = components.map { |c| File.join(self.name.underscore, c) }
    components.each do |c|
      file = File.join(Rails.root, "app/behaviours", c)
      if File.exist?(file + ".rb")
        require file
        klass = File.join("can_has_extensions", c).camelize.constantize
        # Include the appropriate modules.
        include klass::InstanceMethods if defined?(klass::InstanceMethods)
        extend  klass::ClassMethods    if defined?(klass::ClassMethods)
        # Call implemented! if the method exists.
        klass.implemented!(self) if klass.respond_to?(:implement!)
      else
        Rails.logger.warn "Couldn't load behaviour for #{c.camelize} - File not found at #{file}.rb"
      end
    end
  end
  
  private
  
  # Recursively flattens the parameters and extracts paths etc.
  def _flatten_parameters(item, prefix = "")
    extras = []
    if    item.is_a?(Hash)
      extras = item.map do |k,v| 
        extras = _flatten_parameters(v).map { |i| File.join(k.to_s, i) }
      end
    elsif item.is_a?(Array)
      extras = item.map { |i| i.to_s }
    else 
      extras = [item.to_s]
    end
    extras = extras.map { |v| File.join(prefix, v) } unless prefix.blank?
    return extras.flatten
  end
  
end

USAGE.txt

require 'model_extensions'
class X
  extend ModelExtensions
  can_has 'something', 'user' => 'demo'
end

Will try and load CanHasExtensions::X::Something and CanHasExtensions::X::User::Demo
located at app/behaviours/x/something.rb and app/behaviours/x/user/demo.rb