Optimize component transitions without changing the API

src/world.nim

@@ -156,17 +156,22 @@ proc nextArchetypeAddingFrom(world: var World, previousArchetype: Archetype, com
     result = world.archIdToIndex[nextArchetypeId]
 
 
-proc nextArchetypeRemovingFrom(world: var World, previousArchetype: Archetype, componentIdsToRemove: seq[ComponentId]): int =
+proc nextArchetypeRemovingFrom(world: var World, previousArchetype: Archetype, componentIdsToRemove: PackedSet[ComponentId]): int =
   let previousArchetypeId = previousArchetype.id
   var nextArchetypeId = previousArchetypeId
 
-  for componentId in componentIdsToRemove:
+  for componentId in componentIdsToRemove.items:
     nextArchetypeId.excl componentId
 
   result = world.archIdToIndex.getOrDefault(nextArchetypeId, -1)
 
   if result < 0:
-    let newArchetype = previousArchetype.makeNextRemoving(componentIdsToRemove)
+    var componentIds: seq[ComponentId]
+
+    for componentId in componentIdsToRemove.items:
+      componentIds.add componentId
+
+    let newArchetype = previousArchetype.makeNextRemoving(componentIds)
     world.registerArchetype(nextArchetypeId, newArchetype)
 
     result = world.archIdToIndex[nextArchetypeId]
@@ -432,12 +437,8 @@ proc consolidateAddComponents(world: var World, id: EntityId, componentsToAdd: T
 proc consolidateRemoveComponents(world: var World, id: EntityId, compIdsToRemove: PackedSet[ComponentId]) =
   var entity = world.entities[id.value]
   var previousArchetype = world.archetypes[entity.archetypeIndex]
-  var componentIds: seq[ComponentId]
-
-  for compId in compIdsToRemove.items:
-    componentIds.add compId
 
-  let nextIndex = world.nextArchetypeRemovingFrom(previousArchetype, componentIds)
+  let nextIndex = world.nextArchetypeRemovingFrom(previousArchetype, compIdsToRemove)
   var nextArchetype = world.archetypes[nextIndex]
 
   entity.archetypeIndex = nextIndex

tests/tremoval.nim

@@ -0,0 +1,100 @@
+# ISC License
+# Copyright (c) 2025 RowDaBoat
+# `vecs` is a free open source ECS library for Nim.
+import unittest
+import ../src/[examples, vecs]
+
+
+type RemovalPayload = ref object
+  value: string
+
+
+type RetainedComponent = object
+  payload: RemovalPayload
+
+
+suite "Component removal should":
+  test "accept duplicate component types":
+    var world = World()
+    let entityId = world.add((Character(name: "Marcus"), Health(health: 100), Weapon(name: "Sword")), Immediate)
+
+    world.remove(entityId, (Health, Weapon, Health), Immediate)
+
+    check world.has(entityId)
+    check world.read(entityId, Meta).id == entityId
+    check world.read(entityId, Character).name == "Marcus"
+    check not world.has(entityId, Health)
+    check not world.has(entityId, Weapon)
+
+
+  test "retain reference values when removal creates and then reuses a destination":
+    var world = World()
+    let firstPayload = RemovalPayload(value: "First")
+    let secondPayload = RemovalPayload(value: "Second")
+    let firstId = world.add((RetainedComponent(payload: firstPayload), Health(health: 100), Character(name: "Marcus"), Weapon(name: "Sword")), Immediate)
+    let secondId = world.add((RetainedComponent(payload: secondPayload), Health(health: 80), Character(name: "Elena"), Weapon(name: "Staff")), Immediate)
+
+    world.remove(firstId, (Weapon, Health), Immediate)
+    world.remove(secondId, (Health, Weapon), Immediate)
+    GC_fullCollect()
+
+    var query: Query[(Meta, Character, RetainedComponent)]
+    var entityCount = 0
+
+    for (meta, character, retained) in world.query(query):
+      inc entityCount
+      check not world.has(meta.id, Health)
+      check not world.has(meta.id, Weapon)
+
+      if meta.id == firstId:
+        check character.name == "Marcus"
+        check retained.payload == firstPayload
+        check retained.payload.value == "First"
+      else:
+        check meta.id == secondId
+        check character.name == "Elena"
+        check retained.payload == secondPayload
+        check retained.payload.value == "Second"
+
+    check entityCount == 2
+
+
+  test "retain reference values when destination columns have a different order":
+    var world = World()
+    let existingPayload = RemovalPayload(value: "Existing")
+    let movedPayload = RemovalPayload(value: "Moved")
+    let existingId = world.add((Character(name: "Elena"), RetainedComponent(payload: existingPayload)), Immediate)
+    let movedId = world.add((RetainedComponent(payload: movedPayload), Health(health: 100), Character(name: "Marcus"), Weapon(name: "Sword")), Immediate)
+
+    world.remove(movedId, (Weapon, Health), Immediate)
+    GC_fullCollect()
+
+    check world.read(existingId, Character).name == "Elena"
+    check world.read(existingId, RetainedComponent).payload == existingPayload
+    check world.read(existingId, RetainedComponent).payload.value == "Existing"
+    check world.read(movedId, Meta).id == movedId
+    check world.read(movedId, Character).name == "Marcus"
+    check world.read(movedId, RetainedComponent).payload == movedPayload
+    check world.read(movedId, RetainedComponent).payload.value == "Moved"
+    check not world.has(movedId, Health)
+    check not world.has(movedId, Weapon)
+
+
+  test "preserve a pending addition across immediate removal":
+    var world = World()
+    let entityId = world.add((Character(name: "Marcus"), Health(health: 100)), Immediate)
+    world.add(entityId, Weapon(name: "Sword", attack: 10))
+
+    world.remove(entityId, Health, Immediate)
+
+    check not world.has(entityId, Health)
+    check not world.has(entityId, Weapon)
+    check world.read(entityId, Character).name == "Marcus"
+
+    world.consolidate()
+
+    check not world.has(entityId, Health)
+    check world.read(entityId, Meta).id == entityId
+    check world.read(entityId, Character).name == "Marcus"
+    check world.read(entityId, Weapon).name == "Sword"
+    check world.read(entityId, Weapon).attack == 10