player_01.rb

# -*- coding: utf-8 -*-
class Player
  attr_writer :speed

  def initialize(param)
    @position_x = param[:x]
    @position_y = param[:y]
    @speed = param[:speed]
  end

  def move(direction)
    case direction
    when :up
      @position_y -= @speed
    when :down
      @position_y += @speed
    when :left
      @position_x -= @speed
    when :right
      @position_x += @speed
    end
  end
  
  def position
    return @position_x, @position_y
  end
end

player = Player.new(:x => 100, :y => 100, :speed => 10)
player.move(:up)
p player.position # => [100, 90]

player.speed = 20
player.move(:down)
p player.position #=> [100, 110]

速度を状態に持つバージョン