an implementation of ruby's Flatten ... in ruby

array.rb

class Array
  # Performs the same function as 
  # flatten, only slower (because it's in Ruby
  # and .flatten is implemented in C)
  def slow_flatten(arr = self, result = [])
    if arr.size > 0
      first = arr.first
      if ! arr.first.is_a? Array
        result.push(first)
      else
        result.concat( slow_flatten(first, []) )
      end
      return slow_flatten(arr[1..-1], result)
    else
      return result
    end
  end
end

array_spec.rb

require "spec_helper"
require "array"

RSpec.describe Array do
  context "#slow_flatten" do
    it "should not blow up on empty arrays" do
      expect([].slow_flatten).to(eq([]))
    end

    it "should flatten arrays" do
      expect([[1,2,[3]],4].slow_flatten).to(eq([1,2,3,4]))
    end

    it "should not flatten arrays in hashes in arrays" do
      expect([1, 2, [3, 4, [5, 6]], {7=>[8, [9]]}].slow_flatten).to(eq(
        [1, 2, 3, 4, 5, 6, {7=>[8, [9]]}]))
    end
  end
end