Iterating over a hash containing arrays

Last week I was implementing some auditing functionality in a rails app. At some point I was writing a page that would display how the attributes of a given ActiveRecord object had been changed. One of my colleagues spotted this and pointed out the following neat bit of syntactic sugar in Ruby.

changes = {:attribute_a => [1, 2], :attribute_b => [3, 4]}

changes.each do |attribute, (before, after)|
  puts "#{attribute}: #{before} - #{after}"

I later learned you can even do things like this.

data = {:foo => [[1, 2], 3]}

data.each do |key, ((a, b), c)|
  puts "#{key}: #{a} - #{b} - #{c}"