Question

I’ve been trying to dynamically define some instance methods in Ruby 1.9. Here’s the code I’ve been using to try this out:

class Testing
  [:one, :two].each do |name|
    define_method(name) do
      puts __method__
    end
  end
end

And here’s the output:

ruby-1.9.2-p180 :008 > t = Testing.new
 => #<Testing:0x00000100961878> 
ruby-1.9.2-p180 :009 > t.one
two
 => nil 
ruby-1.9.2-p180 :010 > t.two
two
 => nil 
ruby-1.9.2-p180 :011 > 

I would expect the result to be one and two respectively. If I call define_method of each one outside of the iteration it works as expected. What am I not understanding here?

Here is one of many examples I saw around online of define_method being called in an iteration. Dynamically defined setter methods using define_method?

What’s missing?

Also: Using __method__ isn’t critical for me, but it was the best way I could show, that it seems like only the last block sent to define_method is being used for the defined methods. Maybe that is starting to explain the problem to me, but I still don’t understand..

Answer 1

Nice find on the weird behavior. Of all the Rubies I tested, only MRI 1.9.2 demonstrates this.

Ryan Davis has reported the bug on the ruby-core list (referencing this question).