Ruby Trivia

wag_the_dog.rb

class Dog
  def wag(tail=my_tail)
    tail
  end
  def my_tail
    :dogs_tail
  end
end

class Cat
  def wag_dog
    Dog.new.wag
  end
  def my_tail
    :cats_tail
  end
end

puts Cat.new.wag_dog          # What is printed here?
                              # Make a prediction before you try it.

I think any confusion stems from the chained Dog.new.wag

If you instead wrote that your cat wagged its dog thusly:

dog = Dog.new
dog.wag

I hope no one would think that the wag method on dog somehow reaches back to it's caller to get a parameter it wasn't passed...

• its

now with lambdas... (ok, I suck at this)

dog = ->{ :dogs_tail }
cat = ->(dog){ dog.call }
devious_kitty = ->(cat,dog) {|cat| cat.call(dog) }
devious_kitty.call(cat,dog)

Putted even more simply it's all about this:

Foo = Class.new do
  def bar(x=self)
    x
  end
end

Foo.new.bar