Observable Example with TTT

example.rb

require "observer"

class Board
  include Observable

  def initialize
    @grid = [" "] * 9
  end

  def to_s
    separator = "\n---+---+---\n"
    Array.new(3) { row_for(_1) }.join(separator)
  end

  def place_marker(position, marker)
    index_position = position.to_i - 1

    if index_position && @grid[index_position] == " "
      @grid[index_position] = marker
      changed
    end
  end

  def broadcast_state
    notify_observers(to_s)
  end

  private

  def row_for(index)
    first, second, third = @grid.each_slice(3).to_a[index]
    " #{first} | #{second} | #{third}"
  end
end

class Display
  def update(board_string)
    system("clear")
    puts board_string
  end
end


b = Board.new
d = Display.new
b.add_observer(d)

curr_marker = "X"
loop do
  print "Enter your input >> "
  input = gets.chomp
  b.place_marker(input, curr_marker)
  if b.changed?
    b.broadcast_state
    curr_marker = curr_marker == "X" ? "O" : "X"
  end
end