Self contained changetracker

src/init.luau

@@ -935,7 +935,7 @@ do
     setmetatable(it, it)
 
     function world_query(world: World, ...: any): Query
-    	-- breaking?
+    	-- breaking
     	if (...) == nil then
     		error("Missing components")
     	end
@@ -1179,8 +1179,10 @@ function World.new()
 
 	self.ROOT_ARCHETYPE = archetype_of(self, {})
 
+	for i = HI_COMPONENT_ID + 1, EcsRest do
 	   -- Initialize built-in components
-	entity_index_new_id(self.entityIndex, EcsChildOf)
+		entity_index_new_id(self.entityIndex, i)
+	end
 
 	return self
 end

test/tests.luau

@@ -564,34 +564,30 @@ TEST("world", function()
 
 end)
 
+type Tracker<T> = { track: (world: World, fn: (changes: {
+        added: () -> () -> (number, T),
+        removed: () -> () -> number,
+        changed: () -> () -> (number, T, T)
+    }) -> ()) -> ()
+}
 
-TEST("changetracker", function()
+type Entity<T = any> = number & { __nominal_type_dont_use: T }
-    local world = jecs.World.new()
-    local Previous = world:component()
 
-    local function shallowEq(a, b)
+local ChangeTracker: <T>(component: Entity<T>) -> Tracker<T>
-        for k, v in a do
-            if b[k] ~= v then
-                return false
-            end
-        end
-        return true
-    end
 
-    local function ChangeTracker(world, component)
+do
-        local addedComponents = {}
+    local world: World
-        local removedComponents = {}
+    local T
-        local previous = jecs.pair(Previous, component)
+    local PreviousT
-        local isTrivial = nil
+    local addedComponents
+    local removedComponents
+    local isTrivial
+    local added
+    local removed
 
-        local function track(fn)
+    local function changes_added()
-            local added = false
-            local removed = false
-
-            local changes = {}
-            function changes.added()
         added = true
-                local q = world:query(component):without(previous)
+        local q = world:query(T):without(PreviousT)
         return function()
             local id, data = q:next()
             if not id then
@@ -611,8 +607,17 @@ TEST("changetracker", function()
         end
     end
 
-            function changes.changed()
+    local function shallowEq(a, b)
-                local q = world:query(component, previous)
+        for k, v in a do
+            if b[k] ~= v then
+                return false
+            end
+        end
+        return true
+    end
+
+    local function changes_changed()
+        local q = world:query(T, PreviousT)
 
         return function()
             local id, new, old = q:next()
@@ -638,10 +643,10 @@ TEST("changetracker", function()
         end
     end
 
-            function changes.removed()
+    local function changes_removed()
         removed = true
 
-                local q = world:query(previous):without(component)
+        local q = world:query(PreviousT):without(T)
         return function()
             local id = q:next()
             if id then
@@ -651,39 +656,62 @@ TEST("changetracker", function()
         end
     end
 
+    local changes = {
+        added = changes_added,
+        changed = changes_changed,
+        removed = changes_removed,
+    }
+
+    local function track(worldToTrack, fn)
+        world = worldToTrack
+        added = true
+        removed = true
+
         fn(changes)
+
         if not added then
-                for _ in changes.added() do
+            for _ in changes_added() do
             end
         end
 
         if not removed then
-                for _ in changes.removed() do
+            for _ in changes_removed() do
             end
         end
 
         for e, data in addedComponents do
-                world:set(e, previous, if isTrivial then data else table.clone(data))
+            world:set(e, PreviousT, if isTrivial then data else table.clone(data))
         end
 
         for _, e in removedComponents do
-                world:remove(e, previous)
+            world:remove(e, PreviousT)
         end
     end
 
-        return {
+    local tracker = { track = track }
-            track = track
+
-        }
+    function ChangeTracker<T>(component: Entity<T>): Tracker<T>
+        T = component
+        -- We just use jecs.Rest because people will probably not use it anyways
+        PreviousT = jecs.pair(jecs.Rest, T)
+        addedComponents = {}
+        removedComponents = {}
+
+        return tracker
     end
+end
+
+TEST("changetracker", function()
+    local world = jecs.World.new()
 
 	do CASE "should allow change tracking"
-        local Test = world:component()
+        local Test = world:component() :: Entity<{ foo: number }>
-        local TestTracker = ChangeTracker(world, Test)
+        local TestTracker = ChangeTracker(Test)
 
 		local e = world:entity()
 		world:set(e, Test, { foo = 11 })
 
-        TestTracker.track(function(changes)
+        TestTracker.track(world, function(changes)
             local added = 0
             local changed = 0
             local removed = 0
@@ -705,7 +733,7 @@ TEST("changetracker", function()
     	    test.foo = test.foo + 1
      	end
 
-        TestTracker.track(function(changes)
+        TestTracker.track(world, function(changes)
             local added = 0
             local changed = 0
             local removed = 0
@@ -727,7 +755,7 @@ TEST("changetracker", function()
 
         world:remove(e, Test)
 
-        TestTracker.track(function(changes)
+        TestTracker.track(world, function(changes)
             local added = 0
             local changed = 0
             local removed = 0