How to discover the overrided methods in Ruby/Rails?

Question

Hey guys. How do I know the methods that a child class overrided in my super class? I have this:


class Test
  def self.inherited(child)
    # child.overrided_methods???
  end

  def self.foo
  end

  def self.bar
  end
end

def Child < Test
  def self.bar
    puts "bar"
  end
end

The method self.inherited is called when a subclass of Test is loaded. So I get the reference to this subclass in child, but I don't know how to get the methods that were overrided by this subclass.

Any ideas?

--

Arsen suggested the use of self.method_added(name) instead of self.inherited(child), but this method catches only instance methods and I want to catch class methods. Does anyone know another methods that does the same thing but with class methods? In the last case I'll consider using a singleton and convert all this class methods to instance methods then the problem is solved.

To clarify: are you trying to call Child's methods from Test? — Reese Moore
Yes. I want to know what methods Child overrided. They are all class methods and child variable is a reference to the class Child. — Rodrigo Souto
How about the simplest approach: "Child.methods(false) & Test.methods(false)"? The problem is: when do you want to call it? 'Inherited' is called too early. — Arsen7
Ok, I have found the solution. My answer is undeleted and updated. I hope I didn't mess anything this time ;-) — Arsen7

Arsen7 Arsen7 · Accepted Answer · 2010-11-17T14:27:46

For instance methods there is an Object::method_added(name) method you can override, similar to 'inherited' you have used:

class test
  def self.method_added(name)
    puts "method_added(#{name.inspect})"
    super
  end
end

irb(main):002:0> class Child < Test; def foo; end; end
method_added(:foo)
=> nil

You can then compare a received name to a list of your methods:

Test.instance_methods.include?(name.to_s)

With class methods this approach does not work (even if you do things like class << self magic), but a helpful fellow knew the answer: http://www.ruby-forum.com/topic/120416 :

class Test
  def self.singleton_method_added(name)
    puts "Class method added #{name.inspect}"
  end
end

This is only the first part of the problem, because you need to know which class defined the method (it will be self) and whether the method is a new one, or overridden one. Experiment with this code:

class Test
  def self.singleton_method_added(name)
    if self == Test
      puts "My own class method added: #{self.name}.#{name.inspect}"
    elsif Test.methods(false).include?(name.to_s)
      puts "Class method overriden: #{self.name}.#{name.inspect}"
    elsif Test.methods(true).include?(name.to_s)
      puts "My parent's class method overriden: #{self.name}.#{name.inspect}"
    else
      puts "New class method added: #{self.name}.#{name.inspect}"
    end
  end
end

How to discover the overrided methods in Ruby/Rails?

3 Answers