From: Devin Mullins <twifkak@...>
Date: 2005-06-30T10:27:54+09:00
Subject: Re: Q: inheriting from Array, overloading []

Change super[key] to super(key) or super key. Remember, [] is just 
another method, and like other methods, it accepts the typical form.

class A
  def [](key)
    puts "key: #{key}"
  end
end

a = A.new
a.[](5)

Outputs:
key: 5

As matz posted, super defaults to passing the same values passed to you, 
while super() passes zero args.

class A
  def put(a)
    puts a
  end
end
class B<A
  def put(n)
    if n == 0
      super "zero"
    elsif n < 0
      super()
    else
      super
    end
  end
end
b = B.new
b.put 0
b.put 5
b.put -1

Outputs:
zero
5
-:11:in `put': wrong number of arguments (0 for 1) (ArgumentError)
        from -:11:in `put'
        from -:20

So your code was invoking the super method with key as a parameter, 
taking the return value, and then invoking #[](key) on that.

Devin