A simple linked list by 9 lines of code

#ruby #enumerable #datastructure #linkedlist

Today I read Ruby's magical Enumerable module from AppSignal. It clearly explains the subject. And It gives a short code for linked list, I like it.

class LinkedList
  def initialize(head, tail = nil)
    @head, @tail = head, tail
  end

  def <<(item)
    LinkedList.new(item, self)
  end

  def inspect
    [@head, @tail].inspect
  end
end

irb> LinkedList.new(73) << 12 << 42
=> [42, [12, [73, nil]]]

And then with a each method and a include, You can make it Enumerable.

class LinkedList
  include Enumerable

  def initialize(head, tail = nil)
    @head, @tail = head, tail
  end

  def <<(item)
    LinkedList.new(item, self)
  end

  def inspect
    [@head, @tail].inspect
  end

  def each(&block)
    block.call(@head)
    @tail.each(&block) if @tail
  end
end

irb> list = LinkedList.new(73) << 12 << 42
=> [42, [12, [73, nil]]]
irb> list.count
=> 3
irb> list.max
=> 73
irb> list.map { |item| item * item }
=> [1764, 144, 5329]
irb> list.select(&:even?)
=> [42, 12]