Not every object has a position

lib/game_object.rb

@@ -3,7 +3,6 @@
 
 module GeekGame
   class GameObject
-    attr_reader :position
     attr_reader :birth_time
 
     def initialize
@@ -30,9 +29,9 @@ def distance_to(another_object)
     def to_hash
       {
         id: id,
-        type: self.class.to_s.demodulize.underscore,
-        position: position.to_array
+        type: self.class.to_s.demodulize.underscore
       }.tap do |hash|
+        hash[:position] = position.to_array if respond_to?(:position) && position
         hash[:player_color] = player.color if respond_to?(:player) && player
         hash[:angle] = angle if respond_to?(:angle)
       end
@@ -59,11 +58,14 @@ def define_properties(*properties)
 
     protected
 
-    attr_writer :position
     attr_writer :birth_time
 
     def register!
       GeekGame.game_objects << self
     end
+
+    def deregister!
+      GeekGame.game_objects.delete self
+    end
   end
 end

lib/metal_derrick.rb

@@ -5,7 +5,7 @@ class MetalDerrick < Facility
     facility_properties connection_distance: 20
     metal_derrick_properties metal_bars_per_chunk: 5, cooldown_period: 2.0
 
-    attr_reader :metal_bars_available
+    attr_reader :metal_bars_available, :position
     alias :metal_bars_available? :metal_bars_available
 
     def initialize(position:)
@@ -41,7 +41,7 @@ def to_hash
 
     protected
 
-    attr_writer :metal_bars_available
+    attr_writer :metal_bars_available, :position
     attr_accessor :seconds_passed_since_last_extraction
 
     def can_give_metal_to?(bot)

lib/recharger.rb

@@ -4,7 +4,7 @@ class Recharger < Facility
 
     recharger_properties range: 300.0, charge_rate: 0.1
 
-    attr_reader :player
+    attr_reader :player, :position
 
     def initialize(params)
       self.position = params[:position]
@@ -27,6 +27,6 @@ def update(seconds)
 
     protected
 
-    attr_writer :player
+    attr_writer :player, :position
   end
 end

lib/shell.rb

@@ -4,7 +4,7 @@ class Shell < GameObject
     MAX_RANGE = 400
     MAX_DAMAGE = 80
 
-    attr_reader :owner, :angle
+    attr_reader :owner, :angle, :position
 
     def initialize(params={})
       self.angle = params[:angle] || 0
@@ -43,7 +43,7 @@ def hit?(bot)
 
     protected
 
-    attr_writer :owner, :angle
+    attr_writer :owner, :angle, :position
     attr_accessor :initial_position
   end
 end

lib/tracked_bot.rb

@@ -7,6 +7,7 @@ class TrackedBot < GameObject
     attr_reader :battery
     attr_reader :player
     attr_reader :angle
+    attr_reader :position
 
     def track_axis
       Line(left_track_position, right_track_position)
@@ -76,6 +77,7 @@ def normalized_axis_vector
     attr_writer :health_points
     attr_writer :player
     attr_writer :angle
+    attr_writer :position
 
     def advancing_cost(seconds)
       movement_cost * seconds * (left_track.power + right_track.power)