Citrusbyte code sample: Write some code, that will flatten an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].

phils_flatten.rb

#!/usr/bin/env ruby

puts "Hello Citrusbyte!"
puts
puts "Run this file with `ruby phils_flatten.rb -v` and it will automatically run the Minitests."
puts "Also, generate the rdoc with `rdoc phils_flatten.rb` and open ./doc/PhilsFlatten.html."
puts

# Include this module in the Array class to add the method phils_flatten to arrays, which recursively flattens them.
#
#   class Array
#     include PhilsFlatten
#   end
#
module PhilsFlatten
  # I strongly object to not being allowed to cheat during this exercise =P
  #   [[1,2,[3]],4].phils_flatten_cheating == [[1,2,[3]],4].flatten
  #
  def phils_flatten_cheating
    self.flatten
  end

  # This method flattens any enumerable object that responds to the method "each", such as Array.
  #   [[1,2,[3]],4].phils_flatten == [1,2,3,4]
  #
  # my_array.phils_flatten iterates over each of its elements, and then either returns them in order, or recursively calls phils_flatten on elements that themselves need to be flattened.
  def phils_flatten
    flattened = []
    self.each do | item |
      if item.respond_to? :phils_flatten
        # I'm purposefully avoiding the Ruby-ism "array += [other_array]".
        item.phils_flatten.each do | sub_item |
          flattened << sub_item
        end
      else
        flattened << item
      end
    end
    return flattened
  end
end

# This is the Ruby standard library Array.
class Array # :nodoc:
  # Include the PhilsFlatten module into the Array class to add phils_flatten to Array objects.
  include PhilsFlatten
end

# Here we begin testing PhilsFlatten. First require minitest.
require "minitest/autorun"

puts "Testing that [[1,2,[3]],4].phils_flatten == [1,2,3,4]"
puts "Testing that [\"one\", [[2, \"quick brown fox\"]], [1, Time.now, [3] ], 4].phils_flatten == [\"one\", 2, \"quick brown fox\", 1, Time.now, 3, 4]"
puts "Testing that phils_flatten == flatten for @test_array"
puts "Testing that phils_flatten == flatten for @test_array_two"
puts

# This class tests the PhilsFlatten module on Array.
class TestPhilsFlatten < Minitest::Test
  # Sets up two test arrays, a simple one and a complex one.
  def setup
    @current_time   = Time.now
    @test_array     = [[1,2,[3]],4]
    @test_array_two = ["one", [[2, "quick brown fox"]], [1, @current_time, [3] ], 4]
  end

  # Test that a nested array of integers flattens properly.
  #   [[1,2,[3]],4].phils_flatten == [1,2,3,4]
  def test_that_phils_flatten_works_on_test_array
    assert_equal @test_array.phils_flatten, [1, 2, 3, 4]
  end

  # Testing that complicated nested arrays of multiple objects flattens properly.
  #   ["one", [[2, "quick brown fox"]], [1, Time.now, [3] ], 4].phils_flatten == ["one", 2, "quick brown fox", 1, Time.now, 3, 4]
  def test_that_phils_flatten_works_on_test_array_two
    assert_equal @test_array_two.phils_flatten, ["one", 2, "quick brown fox", 1, @current_time, 3, 4]
  end

  # Testing that +phils_flatten+ and +flatten+ are the same for +test_array+.
  #   @test_array.phils_flatten == @test_array.flatten
  def test_that_phils_flatten_equals_builtin_flatten_on_test_array
    assert_equal @test_array.phils_flatten, @test_array.flatten
  end

  # Testing that +phils_flatten+ and +flatten+ are the same for +test_array_two+.
  #   @test_array_two.phils_flatten == @test_array_two.flatten
  def test_that_phils_flatten_equals_builtin_flatten_on_test_array_two
    assert_equal @test_array_two.phils_flatten, @test_array_two.flatten
  end
end