Defining “method_called”.. How do I make a hook method which gets called every time any function of a class gets called?

Question

I want to make a hook method which gets called everytime any function of a class gets called. I have tried method_added, but it executes only once at the time of class defin

Answer 1

I recently wrote something that might be useful, though there are some provisos (see below). Here's the class you want to add your hook to:

class Original  
  def regular_old_method msg
    puts msg
  end

private

  def always_called method_called
    puts "'#{method_called.to_s.capitalize}' method's been called!"
  end
end

And here's the code for adding that hook:

class << Original
  def new(*args)
    inner = self.allocate
    outer_name = self.name + 'Wrapper'
    outer_class = Class.new do
      def initialize inner_object
        @inner = inner_object
      end
      def method_missing method_called, *args
        @inner.send method_called, *args
        @inner.send :always_called, method_called
      end
    end
    outer_class_constant = Object.const_set(outer_name, outer_class)
    inner.send :initialize, *args
    outer_class_constant.new inner
  end
end

If you call it like this...

o = Original.new
o.regular_old_method "nothing unusual about this bit"

You get the following output:

nothing unusual about this bit

'Regular_old_method' method's been called!

This approach would be a bad idea if your code checked class names, because even though you've asked for an object of class 'Original', what you got back was an object of class 'OriginalWrapper'.

Plus I imagine there could be other drawbacks to messing with the 'new' method, but my knowledge of Ruby metaprogramming doesn't stretch that far yet.