Creating a non-empty array in Ruby

non_empty_array.rb

class NonEmptyArray
  include Enumerable

  def initialize(first, rest)
    @first = first
    @rest = rest
  end

  def first
    @first
  end

  def last
    @rest.last || @first
  end

  def each(&block)
    yield @first
    @rest.each(&block)
    self
  end
end

# [1] pry(main)> array = NonEmptyArray.new(1, [2,3,4])
# [2] pry(main)> array.first
# => 1
# [3] pry(main)> array.last
# => 4
# => #<NonEmptyArray:0x00007fcb6db57490 @first=1, @rest=[2, 3, 4]>
# [4] pry(main)> array.each { |n| puts n }
# 1
# 2
# 3
# 4
# => #<NonEmptyArray:0x00007fb3eca3c918 @first=1, @rest=[2, 3, 4]>
# [5] pry(main)> array.map { |n| n * 2 }
# => [2, 4, 6, 8]
# [6] pry(main)> array.select(&:even?)
# => [2, 4]
# [7] pry(main)> array.to_a
# => [1, 2, 3, 4]


# [1] pry(main)> only_one = NonEmptyArray.new(1, [])
# => #<NonEmptyArray:0x00007fcb6db75b20 @first=1, @rest=[]>
# [2] pry(main)> only_one.first
# => 1
# [3] pry(main)> only_one.last
# => 1