game_of_life.rb

class GameOfLife
  def initialize
    @field = Field.new
  end

  def run(fps:)
    loop do
      puts "\e[0;0H\e[2J#{@field}"
      sleep 1.0 / fps
      step
    end
  end

  def step
    prev_field = Marshal.load(Marshal.dump(@field))

    Field::X_RANGE.to_a.product(Field::Y_RANGE.to_a).each do |x, y|
      count = prev_field.neighbours_at(x, y).count(&:alive?)

      prev_cell = prev_field.at(x, y)
      next_cell = @field.at(x, y)

      case
      when prev_cell.alive? && (2..3).cover?(count)
        next_cell.live!
      when prev_cell.dead? && count == 3
        next_cell.live!
      else
        next_cell.die!
      end
    end
  end

  class Field
    WIDTH  = 50
    HEIGHT = 50

    X_RANGE = 0...WIDTH
    Y_RANGE = 0...HEIGHT

    def initialize
      @map = Array.new(HEIGHT).collect{ Array.new(WIDTH).collect{ Cell.new } }
    end

    def at(x, y)
      (X_RANGE.cover?(x) && Y_RANGE.cover?(y)) ? @map[y][x] : nil
    end

    def neighbours_at(x, y)
      [
        at(x - 1, y - 1), at(x, y - 1), at(x + 1, y - 1),
        at(x - 1, y    ),               at(x + 1, y    ),
        at(x - 1, y + 1), at(x, y + 1), at(x + 1, y + 1)
      ].compact
    end

    def to_s
      @map.collect{ |line| "|#{line.collect(&:to_s).join('|')}|" }.join("\n")
    end
  end

  class Cell
    def initialize
      @alive = [true, false].sample
    end

    def live!
      @alive = true
    end

    def die!
      @alive = false
    end

    def alive?
      @alive
    end

    def dead?
      !@alive
    end

    def to_s
      alive? ? '@' : '_'
    end
  end
end

GameOfLife.new.run(fps: 60)