An (unfinished) game of life implementation by @t_crayford and @AvivBY

game_of_life.rb

#Any live cell with fewer than two live neighbours dies, as if caused by under-population.
#Any live cell with two or three live neighbours lives on to the next generation.
#Any live cell with more than three live neighbours dies, as if by overcrowding.
#Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
class Cell
  attr_accessor :x, :y
  def initialize(x,y)
    @x = x
    @y = y
  end

  def neighbour_of?(other_cell)
    close_by?(:x, other_cell) && close_by?(:y, other_cell)
  end

  def close_by?(direction, other_cell)
    (other_cell.send(direction) - self.send(direction)).abs < 2
  end
end

class Grid
  def initialize(*cells)
    @cells = cells
  end

  def alive_neighbours_around(cell)
    @cells.select { |c| c.neighbour_of?(cell) }.size - 1
  end
end

describe 'counting live neighbours' do
  let(:center_cell) { Cell.new(0,0) }
  it 'returns zero alive neighbours around a lonely cell' do
    grid = Grid.new(center_cell)
    grid.alive_neighbours_around(center_cell).should == 0
  end

  it 'alive_neighbours_around should probably be named something else'

  it 'returns one alive neighbour around a cell with one neighbour' do
    grid = Grid.new(Cell.new(1,0), center_cell)
    grid.alive_neighbours_around(center_cell).should == 1
  end

  it 'returns one alive neighbour around a cell with one neighbour, and one distant cousin' do
    grid = Grid.new(Cell.new(1,0), center_cell, Cell.new(100,100))
    grid.alive_neighbours_around(center_cell).should == 1
  end

  it 'returns 0 for a far away northern cousin' do
    grid = Grid.new(Cell.new(0,100), center_cell)
    grid.alive_neighbours_around(center_cell).should == 0
  end
end