Question

For (auto-)educational purposes, I’m trying to mimic the super behavior to learn how it works.

I could mimic super for instance methods, but I couldn’t do it for class methods.

Here is my code:

class A
  def aa
    @msg ||= 'Original...: '
    puts "#{@msg}#{self}.aa: #{self.class} < #{self.class.superclass}"
  end
  def self.ab
    @msg ||= 'Original...: '
    puts "#{@msg}#{self}.ab: #{self} < #{self.superclass}"
  end
end

class B < A
  def aa
    @msg = "Real super.: "
    super
  end
  def self.ab
    @msg = "Real super.: "
    super
  end
  def mimic_aa
    @msg = "Mimic super: "
    self.class.superclass.instance_method(:aa).bind(self).call
  end
  def self.mimic_ab
    @msg = "Mimic super: "
    #superclass.method(:ab).unbind.bind(self).call
      #=> Error: singleton method only works in original object

    #superclass.ab
      #=> self is A; I want self to be B

    proc = superclass.method(:ab).to_proc

    #self.instance_eval(&proc)
      #=> ArgumentError: instance_eval seems to call aa(some_unwanted_param)
      # Note: Ruby 1.8.7

    #eval('proc.call', binding)
      #=> self is A; I want self to be B

  end
end

a = A.new
b = B.new

a.aa         #=> Original...: #<A:0xb77c66ec>.aa: A < Object
b.aa         #=> Real super.: #<B:0xb77c6624>.aa: B < A
b.mimic_aa   #=> Mimic super: #<B:0xb77c6624>.aa: B < A

puts ''

A.ab         #=> Original...: A.ab: A < Object
B.ab         #=> Real super.: B.ab: B < A
B.mimic_ab   #=> (expected the same as above)

Any ideas?

Answer 1

Well, the problem is probably the version of Ruby that you are using. I’m running 1.9.2, and the program runs as expected. I think (from the comment in your code) that the problem is that you are running Ruby v1.8.7. It also wouldn’t hurt to try running your code again.