First pass at Conway's Game of Life implementation with @thecommongeek

game_of_life_spec.rb

require 'rspec'

class Life
  def initialize
    @cells = [
      [Cell.new, Cell.new, Cell.new],
      [Cell.new, Cell.new, Cell.new],
      [Cell.new, Cell.new, Cell.new],
    ]
  end

  def make_alive(cell)
    @cells[cell.y][cell.x] = cell
  end

  def lifecycle
    @cells.each.with_index do |row, y|
      row.each.with_index do |cell, x|
      end
    end
  end

  def live_cells
    @cells.flatten.select(&:alive?)
  end
end

class Cell
  def initialize(options={})
    @alive = options.fetch(:alive, false)
    @x = options.fetch(:x, nil)
    @y = options.fetch(:y, nil)
  end

  attr_accessor :number_of_neighbors, :x, :y

  def alive?
    @alive
  end

  def lifecycle
    if number_of_neighbors < 2
      @alive = false
    elsif number_of_neighbors > 3
      @alive = false
    elsif number_of_neighbors == 3
      @alive = true
    end
  end

  def coords
    [@x, @y]
  end
end

describe Life do
  describe "board" do
    it "has many cells" do
      game = Life.new
      game.make_alive Cell.new(x: 0, y: 1, alive: true)
      game.make_alive Cell.new(x: 1, y: 1, alive: true)
      game.make_alive Cell.new(x: 2, y: 1, alive: true)

      game.lifecycle

      game.live_cells.map(&:coords).should include [1, 0]
      game.live_cells.map(&:coords).should_not include [0, 1]
    end
  end

  describe "live cells" do
    let(:cell)  { Cell.new(alive: true) }

    it "dies if less than 2 live neighbors" do
      cell.should be_alive
      cell.number_of_neighbors = 1
      cell.lifecycle
      cell.should_not be_alive
    end

    it "dies if more than 3 neighbors, as if by overcrowding" do
      cell.should be_alive
      cell.number_of_neighbors = 4
      cell.lifecycle
      cell.should_not be_alive
    end

    it "lives if it has only 2 neighbors" do
      cell.should be_alive
      cell.number_of_neighbors = 2
      cell.lifecycle
      cell.should be_alive
    end

    it "lives if it has only 3 neighbors" do
      cell.should be_alive
      cell.number_of_neighbors = 3
      cell.lifecycle
      cell.should be_alive
    end
  end

  describe "dead cells" do
    it "becomes alive if exactly 3 live neighbors" do
      cell = Cell.new(alive: false)
      cell.should_not be_alive
      cell.number_of_neighbors = 3
      cell.lifecycle
      cell.should be_alive
    end
  end
end