gistfile1.rb

Trying to create a little proxy around a class:

class Bar
	def self.foo
		"mark"
	end
end

It works by opening the class:

class Bar
   class << self
      alias_method :orig, :foo
      def foo
         p "i am overriden"
         orig
      end
   end
end

But I want to only create the proxy on a method call so trying to use 'define_method' instead:

Bar.send(:alias_method, :orig, :foo)

But that fails saying:

NameError: undefined method `foo' for class `Bar'
	from (irb):11:in `alias_method'
	from (irb):11:in `send'
	from (irb):11
	from :0

Must be doing something obvious wrong but not sure what

I think you need call the send on the metaclass of bar. Something like this works....

class Bar
  def self.foo
    "mark"
  end

  def self.metaclass
    class << self; self; end
  end
end

Bar.metaclass.send :alias_method, :orig, :foo
Bar.orig # "mark"`

foo is not an instance method of Bar so it won't work. You'll need to use instance_eval or class_eval on Bar or the above technique of metaclass (never seen it before, thanks joelash).

http://gist.github.com/573343

Ok I get it now. Shouldn't the metaclass be called the eigen class though?

Yes they are synonyms. In my experience you'll hear people call it either.

OK mark just pointed out a typo in my example and I cannot edit it on an iPhone so I'll fix it when I get to a real computer but the secon to last line should be
Bar.metaclass.send :alias_method, :orig, :foo

joelash: They aren't synonyms, though in ruby they are often used as such. In this case eigenclass would be more accurate iirc, though I used metaclass.

kalwre: you're right I should have been more specific in saying in ruby they're considered synonyms. Thanks for the correction!