March 11, 2011

Define Your Inner Foo

Recently attended a great talk by Paul Barry at the DCRUG. During his talk, he wondered off into defining a method in a method.

This was really cool.

I took some time playing with this, and after showing a few colleagues, I had to write this up. I encourage you to fire up IRB and try it your self. This is probably not something you would actually want to do in a project, but once you know about it then you will be tempted to find a problem for this solution.

define_your_inner_foo.rb:

class DefineYourInnerFoo
  def foo
    def foo
      def foo
        "Zirbert"
      end
      "Zaz"
    end
    "Zing"
  end
end

irb:

>> load 'define_your_inner_foo.rb'
>> f = DefineYourInnerFoo.new
>> f.foo #=> 'Zing'
>> f.foo #=> 'Zaz'
>> f.foo #=> 'Zirbert'
>> f.foo #=> 'Zirbert'
>> g = DefineYourInnerFoo.new
>> g.foo #=> 'Zirbert'
>> g.foo #=> 'Zirbert'

A slightly more contrived example:

animal.rb:

class Animal
  def speak
    "Hello, I am a Animal"
  end
  def be_dog
    def speak
      "Woof"
    end
  end
  def be_bird
    def speak
      "Tweet-a-leet"
    end
  end
  def be_whale
    def speak
      "HeeeeeeiiilllllllloooooooooOOOOOOooo....oooooOOOOoo"
    end
  end
end

irb:

>> load 'animal.rb' #=> true
>> a = Animal.new #=> #<Animal:0x00000101126900>
>> a.speak #=> "Hello, I am a Animal"
>> a.be_dog #=> nil
>> a.speak #=> "Woof"
>> a.be_bird #=> nil
>> a.speak #=> "Tweet-a-leet"
>> b = Animal.new #=> #<Animal:0x000001010eeeb0>
>> b.speak #=> "Tweet-a-leet"
>> b.be_whale #=> nil
>> a.speak #=> "HeeeeeeiiilllllllloooooooooOOOOOOooo....oooooOOOOoo"
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