Ruby implementation of flatten for nested arrays

matts-flatten.rb

#!/usr/bin/env ruby

class Array
  def mattflat
    if empty? # base case
      self
    else
      tail = pop
      if tail.kind_of? Array
        mattflat + tail.mattflat
      else
        mattflat << tail
      end
    end
  end
end

class FunArray < Array
  def play
    puts "have fun!"
  end
end


puts "Specs"
puts "====="

f = FunArray.new(2)
f[0] = 1
f[1] = FunArray.new(2)
f[1][0] = 2
f[1][1] = 3

cases = [
  [],
  [1],
  [1, 2, 3],
  [1, [2, 3]],
  [1, [2, [3, 4]]],
  [1, [2, [3, 4], [5, 6, [7, 8, [9, 10, 11], [12]]]], 13, [14, 15], [16]],
  f
]

cases.each_with_index do |c, i|
  print "#{i}. "; print c; puts
  d = c.dup
  a = d.flatten
  r = c.mattflat
  print "r: "; print r; puts
  print "a: "; print a; puts
  puts (r == a) ? "pass" : "fail"
end