Allowed for entities to be in multiple systems. Fixed the removal issue.

fluid/entity.lua

@@ -1,3 +1,7 @@
+local PATH = (...):gsub('%.[^%.]+$', '')
+
+local List = require(PATH..".list")
+
 local Entity = {}
 Entity.__index = Entity
 
@@ -6,7 +10,8 @@ Entity.__index = Entity
 function Entity.new()
    local e = setmetatable({
       components = {},
-      instance   = nil,
+      removed    = {},
+      instances  = List(),
    }, Entity)
 
    return e
@@ -26,15 +31,27 @@ end
 -- @param component The Component to remove
 -- @return self
 function Entity:remove(component)
-   self.components[component] = nil
+   self.removed[component] = true
 
    return self
 end
 
+function Entity:destroy()
+   for i = 1, self.instances.size do
+      self.instances:get(i):removeEntity(self)
+   end
+end
+
 --- Checks the Entity against the pools again.
 -- @return self
-function Entity:check()
+function Entity:apply()
-   self.instance:checkEntity(self)
+   for i = 1, self.instances.size do
+      self.instances:get(i):checkEntity(self)
+   end
+
+   for _, component in pairs(self.removed) do
+      self.components[component] = nil
+   end
 
    return self
 end

fluid/instance.lua

@@ -19,7 +19,7 @@ function Instance.new()
 end
 
 function Instance:addEntity(e)
-   e.instance = self
+   e.instances:add(self)
    self.entities:add(e)
    self:checkEntity(e)
 end
@@ -31,6 +31,7 @@ function Instance:checkEntity(e)
 end
 
 function Instance:removeEntity(e)
+   e.instances:remove(self)
    self.entities:remove(e)
 
    for _, system in ipairs(self.systems) do

fluid/pool.lua

@@ -16,7 +16,7 @@ end
 
 function Pool:eligible(e)
    for _, component in ipairs(self.filter) do
-      if not e.components[component] then
+      if not e.components[component] or e.removed[component] then
          return false
       end
    end

fluid/system.lua

@@ -86,7 +86,7 @@ function System:__tryAdd(e)
    self.__all[e] = self.__all[e] + 1
 end
 
-function System:__tryRemove()
+function System:__tryRemove(e)
    if self:__has(e) then
       self.__all[e] = self.__all[e] - 1
 

main.lua

@@ -76,13 +76,13 @@ end
 function RandomRemover:update(dt)
    self.time = self.time + dt
 
-   if self.time >= 0.5 then
+   if self.time >= 0.25 then
       self.time = 0
 
       if self.pool.size > 0 then
          local i = love.math.random(1, self.pool.size)
 
-         Game:removeEntity(self.pool.objects[i])
+         self.pool:get(i):destroy()
       end
    end