Removed the need for manual flushing. Systems now know about their instance

fluid/instance.lua

@@ -52,6 +52,7 @@ end
 --- Completely removes all marked Entities in the Instance.
 -- @return self
 function Instance:flush()
+   if #self.removed > 0 then
       for i = 1, #self.removed do
          local e = self.removed[i]
 
@@ -64,6 +65,7 @@ function Instance:flush()
       end
 
       self.removed = {}
+   end
 
    return self
 end
@@ -75,8 +77,13 @@ end
 -- @param enabled If the system is enabled. Defaults to true
 -- @return self
 function Instance:addSystem(system, eventName, callback, enabled)
+   if system.__instance then
+      error("System already in instance '" ..system.__instance.."'")
+   end
+
    if not self.systems:has(system) then
       self.systems:add(system)
+      system.__instance = self
    end
 
    if eventName then
@@ -141,6 +148,8 @@ end
 -- @param ... Parameters passed to listeners
 -- @return self
 function Instance:emit(eventName, ...)
+   self:flush()
+   
    local listeners = self.events[eventName]
 
    if listeners then

fluid/system.lua

@@ -129,6 +129,12 @@ function System:__tryRemove(e)
    end
 end
 
+--- Returns the Instance the System is in.
+-- @return The Instance
+function System:getInstance()
+   return self.__instance
+end
+
 --- Returns if the System has the Entity.
 -- @param The Entity to check for
 -- @return True if the System has the Entity. False otherwise

main.lua

@@ -89,21 +89,10 @@ function RandomRemover:update(dt)
    love.window.setTitle(love.timer.getFPS())
 end
 
-local RemovalSystem = System({})
-function RemovalSystem:init(instance)
-   self.instance = instance
-end
-
-function RemovalSystem:update()
-   self.instance:flush()
-end
-
 Game:addSystem(RandomRemover(),     "update")
 Game:addSystem(RectangleRenderer(), "draw")
 Game:addSystem(CircleRenderer(),    "draw")
 
-Game:addSystem(RemovalSystem(Game), "update", false)
-
 for i = 1, 100 do
    local e = Entity()
    e:give(Position, love.math.random(0, 700), love.math.random(0, 700))