postels_law_5.rb

Array(nil)  # => []
Array(1)    # => [1]
Array([3])  # => [3]


class ArrayLikeThing
  def to_a
    [1, 2, 3]
  end

  # defining to_ary is required for Array() casting to work.
  alias :to_ary :to_a
end

thing = ArrayLikeThing.new
Array(thing)  # => [1, 2, 3]