Flatten an array of arbitrarily nested arrays of integers into a flat array of integers in ruby

array-flatter.rb

#!/usr/bin/env ruby

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


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

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]],
  [[[1], 2], 3]
]

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