Question

I am developing a Gem that will allow users to auto-require, instantiate, and register classes in a specific directory. I’m just not sure how to achieve this. This is what I’ve come up with so far…

Dir[Dir.pwd + '/extensions/*.rb'].each do |file|
  require file
  extension_class = # instantiate the class here
  MyApp.extensions << extension_class
end

How can I instantiate the class without knowing what it is called?

Answer 1

It sounds like you are making a system for writing extensions to software. Since the extension classes are probably all similar in some way, such as sharing some common methods, it might make sense to have a base class called Extension from which all the extension classes inherit.

In fact, this is very useful to the stated problem because when a user inherits from your class you can detect it, and add the subclass to a list. Here is some proof of concept code:

class Extension
  class << self
    attr_reader :list
  end
  @list = []

  def self.inherited(klass)
    @list << klass.new
  end
end

# The MyExt class would be in another file, loaded by require.
class MyExt < Extension
end

p Extension.list   # => [#<MyExt:0xb777d884>]

If you don’t want to use subclassing for some reason, it is equally easy to make Extension be a module and use the included hook instead of inherited.

Personally, I would just remove the call to .new because I don’t see a reason to instantiate the class right away, but that’s up to you. I would just store a list of classes.