Coding exercise: Flatten an array in Ruby w/o using `Array#flatten`

flatten-it.rb

module ArrayUtils
  def self.flatten(array, result=[])
    array = Array(array)
    array.each do |entry|
      case entry
      when Array
        flatten entry, result
      else
        result << entry
      end
    end

    result
  end
  
  def self.non_recursive_flatten(array)
    result = []
    enum = array.each
    stack = []

    loop do
      begin
        entry = enum.next
        case entry
        when Array
          stack << enum
          enum = entry.each
        else
          result << entry
        end
      rescue StopIteration
        enum = stack.pop
        break unless enum
      end
    end

    result
  end
end

p ArrayUtils.flatten( [[1,2,[3]],4] )
# => [1, 2, 3, 4]

p ArrayUtils.non_recursive_flatten( [[1,2,[3]],[],4] )
# => [1, 2, 3, 4]