Tic Tac Toe solution in Ruby

tic_tac_toe.rb

class TicTacToeBoard
    SYMBOLS = ['X', 'Y']
    WINNING = [
        [0,1,2], [3,4,5], [6,7,8],
        [0,3,6], [1,4,7], [2,5,8],
        [0,4,8], [2,4,6]
    ]
    def initialize()
        @board = [['','',''], ['','',''], ['','','']]
    end
    
    def move(symbol, x, y)
        return if (x> 2 || y>2) && !SYMBOLS.include?(symbol)
        @board[x][y] = symbol
    end
    
    def draw_board
        @board.each_with_index do |dim1, outer|
            dim1.each_with_index do |_dim2, inner|
                print "#{@board[outer][inner]} "
            end
            puts
        end
    end
    
    def check_winner
        return 'X' if winner?('X')
        return 'O' if winner?('Y')
    end
    
    private
    def winner?(symbl)
      WINNING.any? { |win| win.all? {|pos| fetch_symbol(pos) == symbl } }
    end
  
    def fetch_symbol(index)
        @board[index%3][index/3]
    end
end

ttt = TicTacToeBoard.new
ttt.move("X", 0, 0)
ttt.move("O", 0, 2)
ttt.move("X", 1, 0)
ttt.move("O", 1, 2)
ttt.move("X", 2, 0)

ttt.draw_board # display the board
ttt.check_winner # should return the winner, "X"

# fptr = File.open(ENV['OUTPUT_PATH'], 'w')