From 4bb7e64edddb99eea392ff928831afbc945ce2c1 Mon Sep 17 00:00:00 2001
From: Ukendio <ukendio@gmail.com>
Date: Thu, 8 May 2025 23:21:38 +0200
Subject: [PATCH] Define behaviour for world:entity(id)

---
 addons/observers.luau      | 14 +++++++-------
 jecs.luau                  | 10 +++++++---
 test/addons/observers.luau |  1 -
 test/tests.luau            | 12 ++++++------
 4 files changed, 20 insertions(+), 17 deletions(-)

diff --git a/addons/observers.luau b/addons/observers.luau
index ef85d85..0175060 100644
--- a/addons/observers.luau
+++ b/addons/observers.luau
@@ -1,16 +1,16 @@
 local jecs = require("@jecs")
 
-type Observer<T...> = {
+type Observer = {
 	callback: (jecs.Entity) -> (),
-	query: jecs.Query<T...>,
+	query: jecs.Query<...jecs.Id>,
 }
 
 export type PatchedWorld = jecs.World & {
-	added: <T>(PatchedWorld, jecs.Id<T>, (e: jecs.Entity, id: jecs.Id, value: T) -> ()) -> () -> (),
-	removed: <T>(PatchedWorld, jecs.Id<T>, (e: jecs.Entity, id: jecs.Id) -> ()) -> () -> (),
-	changed: <T>(PatchedWorld, jecs.Id<T>, (e: jecs.Entity, id: jecs.Id, value: T) -> ()) -> () -> (),
-	observer: (PatchedWorld, Observer<any>) -> (),
-	monitor: (PatchedWorld, Observer<any>) -> (),
+	added: <T>(PatchedWorld, jecs.Id<T>, (jecs.Entity, jecs.Id, T) -> ()) -> () -> (),
+	removed: <T>(PatchedWorld, jecs.Id<T>, (jecs.Entity, jecs.Id) -> ()) -> () -> (),
+	changed: <T>(PatchedWorld, jecs.Id<T>, (jecs.Entity, jecs.Id, T) -> ()) -> () -> (),
+	observer: (PatchedWorld, Observer) -> (),
+	monitor: (PatchedWorld, Observer) -> (),
 }
 
 local function observers_new(world, description)
diff --git a/jecs.luau b/jecs.luau
index 35cf16a..f705f0e 100644
--- a/jecs.luau
+++ b/jecs.luau
@@ -780,7 +780,11 @@ local function world_entity(world: ecs_world_t, entity: i53?): i53
 
 			local any = dense_array[dense]
 			if dense <= alive_count then
-				return any
+				if any ~= entity then
+					error("Entity ID is already in use with a different generation")
+				else
+					return entity
+				end
 			end
 
 			local e_swap = dense_array[dense]
@@ -790,9 +794,9 @@ local function world_entity(world: ecs_world_t, entity: i53?): i53
 			r_swap.dense = dense
 			r.dense = alive_count
 			dense_array[dense] = e_swap
-			dense_array[alive_count] = any
+			dense_array[alive_count] = entity
 
-			return any
+			return entity
 		else
 			for i = max_id + 1, index do
 				sparse_array[i]	= { dense = i } :: ecs_record_t
diff --git a/test/addons/observers.luau b/test/addons/observers.luau
index 1d5a99e..b255625 100644
--- a/test/addons/observers.luau
+++ b/test/addons/observers.luau
@@ -23,7 +23,6 @@ TEST("addons/observers", function()
 		world:set(world:entity(), A, true)
 
 		CHECK(count == 3)
-		print(count)
 	end
 
 	do CASE "Ensure ordering between signals and observers"
diff --git a/test/tests.luau b/test/tests.luau
index 61c089d..9ce5023 100644
--- a/test/tests.luau
+++ b/test/tests.luau
@@ -672,7 +672,7 @@ TEST("world:range()", function()
 		local e2v1 = world:entity(399)
 		CHECK(world:contains(e2v1))
 		CHECK(ECS_ID(e2v1) == 399)
-		CHECK(ECS_GENERATION(e2v1) == 1)
+		CHECK(ECS_GENERATION(e2v1) == 0)
 	end
 
 	do CASE "over range start"
@@ -685,12 +685,12 @@ TEST("world:range()", function()
 		local e2v1 = world:entity(405)
 		CHECK(world:contains(e2v1))
 		CHECK(ECS_ID(e2v1) == 405)
-		CHECK(ECS_GENERATION(e2v1) == 1)
+		CHECK(ECS_GENERATION(e2v1) == 0)
 
-		do
-			local _e2v1 = world:entity(405)
-			CHECK(_e2v1 == e2v1)
-		end
+		world:delete(e2v1)
+		local e2v2 = world:entity(e2v1)
+		CHECK(ECS_ID(e2v2) == 405)
+		CHECK(ECS_GENERATION(e2v2) == 0)
 	end
 end)