experimenting with filtering relations

LICENSE.txt

@@ -1,23 +0,0 @@
-MoonTools.ECS - A very simple ECS system for C#
-
-Copyright (c) 2022-2023 Evan Hemsley
-
-This software is provided 'as-is', without any express or implied warranty.
-In no event will the authors be held liable for any damages arising from
-the use of this software.
-
-Permission is granted to anyone to use this software for any purpose,
-including commercial applications, and to alter it and redistribute it
-freely, subject to the following restrictions:
-
-1. The origin of this software must not be misrepresented; you must not
-claim that you wrote the original software. If you use this software in a
-product, an acknowledgment in the product documentation would be
-appreciated but is not required.
-
-2. Altered source versions must be plainly marked as such, and must not be
-misrepresented as being the original software.
-
-3. This notice may not be removed or altered from any source distribution.
-
-Evan "cosmonaut" Hemsley <evan@moonside.games>

MoonTools.ECS.csproj

@@ -1,8 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
+    <TargetFrameworks>net6.0;net7.0</TargetFrameworks>
     <Nullable>enable</Nullable>
+    <Platforms>x64</Platforms>
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
   </PropertyGroup>
 

src/Collections/IndexableSet.cs

@@ -1,106 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
-namespace MoonTools.ECS.Collections;
-
-public unsafe class IndexableSet<T> : IDisposable where T : unmanaged
-{
-	private Dictionary<T, int> Indices;
-	private T* Array;
-	public int Count { get; private set; }
-	private int Capacity;
-	private bool IsDisposed;
-
-	public Span<T> AsSpan() => new Span<T>(Array, Count);
-	public ReverseSpanEnumerator<T> GetEnumerator() => new ReverseSpanEnumerator<T>(new Span<T>(Array, Count));
-
-	public IndexableSet(int capacity = 32)
-	{
-		this.Capacity = capacity;
-		Count = 0;
-
-		Indices = new Dictionary<T, int>(capacity);
-		Array = (T*) NativeMemory.Alloc((nuint) (capacity * Unsafe.SizeOf<T>()));
-	}
-
-	public T this[int i] => Array[i];
-
-	public bool Contains(T element)
-	{
-		return Indices.ContainsKey(element);
-	}
-
-	public bool Add(T element)
-	{
-		if (!Contains(element))
-		{
-			Indices.Add(element, Count);
-
-			if (Count >= Capacity)
-			{
-				Capacity *= 2;
-				Array = (T*) NativeMemory.Realloc(Array, (nuint) (Capacity * Unsafe.SizeOf<T>()));
-			}
-
-			Array[Count] = element;
-			Count += 1;
-
-			return true;
-		}
-
-		return false;
-	}
-
-	public bool Remove(T element)
-	{
-		if (!Contains(element))
-		{
-			return false;
-		}
-
-		var index = Indices[element];
-
-		for (var i = index; i < Count - 1; i += 1)
-		{
-			Array[i] = Array[i + 1];
-			Indices[Array[i]] = i;
-		}
-
-		Indices.Remove(element);
-		Count -= 1;
-
-		return true;
-	}
-
-	public void Clear()
-	{
-		Indices.Clear();
-		Count = 0;
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			NativeMemory.Free(Array);
-			Array = null;
-
-			IsDisposed = true;
-		}
-	}
-
-	~IndexableSet()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: false);
-	}
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
-	}
-}

src/Collections/NativeArray.cs

@@ -1,120 +0,0 @@
-using System;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
-namespace MoonTools.ECS.Collections;
-
-public unsafe class NativeArray<T> : IDisposable where T : unmanaged
-{
-	private T* Elements;
-	public int Count { get; private set;}
-	private int Capacity;
-	private int ElementSize;
-
-	public Span<T> ToSpan() => new Span<T>(Elements, Count);
-	public Span<T>.Enumerator GetEnumerator() => new Span<T>(Elements, Count).GetEnumerator();
-
-	private bool IsDisposed;
-
-	public NativeArray(int capacity = 16)
-	{
-		this.Capacity = capacity;
-		ElementSize = Unsafe.SizeOf<T>();
-		Elements = (T*) NativeMemory.Alloc((nuint) (capacity * ElementSize));
-		Count = 0;
-	}
-
-	public ref T this[int i] => ref Elements[i];
-
-	public void Append(T item)
-	{
-		if (Count >= Capacity)
-		{
-			Capacity *= 2;
-			Elements = (T*) NativeMemory.Realloc(Elements, (nuint) (Capacity * Unsafe.SizeOf<T>()));
-		}
-
-		Elements[Count] = item;
-		Count += 1;
-	}
-
-	public void RemoveLastElement()
-	{
-		Count -= 1;
-	}
-
-	public bool TryPop(out T element)
-	{
-		if (Count > 0)
-		{
-			element = Elements[Count - 1];
-			Count -= 1;
-			return true;
-		}
-
-		element = default;
-		return false;
-	}
-
-	public void Clear()
-	{
-		Count = 0;
-	}
-
-	private void ResizeTo(int size)
-	{
-		Capacity = size;
-		Elements = (T*) NativeMemory.Realloc((void*) Elements, (nuint) (ElementSize * Capacity));
-	}
-
-	// Fills gap by copying final element to the deleted index
-	public void Delete(int index)
-	{
-		if (index != Count - 1)
-		{
-			this[index] = this[Count - 1];
-		}
-
-		Count -= 1;
-	}
-
-	public void CopyTo(NativeArray<T> other)
-	{
-		if (Count >= other.Capacity)
-		{
-			other.ResizeTo(Count);
-		}
-
-		NativeMemory.Copy(
-			(void*) Elements,
-			(void*) other.Elements,
-			(nuint) (ElementSize * Count)
-		);
-
-		other.Count = Count;
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			NativeMemory.Free(Elements);
-			Elements = null;
-
-			IsDisposed = true;
-		}
-	}
-
-	~NativeArray()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: false);
-	}
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
-	}
-}

src/Collections/NativeArrayUntyped.cs

@@ -1,121 +0,0 @@
-using System;
-using System.Runtime.CompilerServices;
-using System.Runtime.InteropServices;
-
-namespace MoonTools.ECS.Collections;
-
-internal unsafe class NativeArray : IDisposable
-{
-	private nint Elements;
-	public int Count { get; private set;}
-	private int Capacity;
-	public readonly int ElementSize;
-
-	private bool IsDisposed;
-
-	public NativeArray(int elementSize)
-	{
-		Capacity = 16;
-		Count = 0;
-		ElementSize = elementSize;
-
-		Elements = (nint) NativeMemory.Alloc((nuint) (ElementSize * Capacity));
-	}
-
-	public Span<T> ToSpan<T>()
-	{
-		return new Span<T>((void*) Elements, Count);
-	}
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	public ref T Get<T>(int i) where T : unmanaged
-	{
-		return ref ((T*) Elements)[i];
-	}
-
-	public void Set<T>(int i, in T element) where T : unmanaged
-	{
-		Unsafe.Write((void*) (Elements + ElementSize * i), element);
-	}
-
-	private void Resize()
-	{
-		Capacity *= 2;
-		Elements = (nint) NativeMemory.Realloc((void*) Elements, (nuint) (ElementSize * Capacity));
-	}
-
-	private void ResizeTo(int capacity)
-	{
-		Capacity = capacity;
-		Elements = (nint) NativeMemory.Realloc((void*) Elements, (nuint) (ElementSize * Capacity));
-	}
-
-	// Fills gap by copying final element to the deleted index
-	public void Delete(int index)
-	{
-		if (index != Count - 1)
-		{
-			NativeMemory.Copy(
-				(void*) (Elements + ((Count - 1) * ElementSize)),
-				(void*) (Elements + (index * ElementSize)),
-				(nuint) ElementSize
-			);
-		}
-
-		Count -= 1;
-	}
-
-	public void Append<T>(T component) where T : unmanaged
-	{
-		if (Count >= Capacity)
-		{
-			Resize();
-		}
-
-		((T*) Elements)[Count] = component;
-		Count += 1;
-	}
-
-	public void CopyAllTo(NativeArray other)
-	{
-		if (Count >= other.Capacity)
-		{
-			other.ResizeTo(Count);
-		}
-
-		NativeMemory.Copy(
-			(void*) Elements,
-			(void*) other.Elements,
-			(nuint) (ElementSize * Count)
-		);
-
-		other.Count = Count;
-	}
-
-	public void Clear()
-	{
-		Count = 0;
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			NativeMemory.Free((void*) Elements);
-			IsDisposed = true;
-		}
-	}
-
-	~NativeArray()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: false);
-	}
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
-	}
-}

src/ComponentDepot.cs

@@ -0,0 +1,129 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace MoonTools.ECS
+{
+	internal class ComponentDepot
+	{
+		private TypeIndices ComponentTypeIndices;
+
+		private ComponentStorage[] storages = new ComponentStorage[256];
+
+		public ComponentDepot(TypeIndices componentTypeIndices)
+		{
+			ComponentTypeIndices = componentTypeIndices;
+		}
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		internal void Register<TComponent>(int index) where TComponent : unmanaged
+		{
+			if (index >= storages.Length)
+			{
+				Array.Resize(ref storages, storages.Length * 2);
+			}
+
+			storages[index] = new ComponentStorage<TComponent>();
+		}
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		private ComponentStorage<TComponent> Lookup<TComponent>() where TComponent : unmanaged
+		{
+			var storageIndex = ComponentTypeIndices.GetIndex<TComponent>();
+			// TODO: is there some way to avoid this null check?
+			if (storages[storageIndex] == null)
+			{
+				Register<TComponent>(storageIndex);
+			}
+			return (ComponentStorage<TComponent>) storages[storageIndex];
+		}
+
+		public bool Some<TComponent>() where TComponent : unmanaged
+		{
+			return Lookup<TComponent>().Any();
+		}
+
+		public ref readonly TComponent Get<TComponent>(int entityID) where TComponent : unmanaged
+		{
+			return ref Lookup<TComponent>().Get(entityID);
+		}
+
+		public ref readonly TComponent GetFirst<TComponent>() where TComponent : unmanaged
+		{
+			return ref Lookup<TComponent>().GetFirst();
+		}
+
+		public void Set<TComponent>(int entityID, in TComponent component) where TComponent : unmanaged
+		{
+			Lookup<TComponent>().Set(entityID, component);
+		}
+
+		public Entity GetSingletonEntity<TComponent>() where TComponent : unmanaged
+		{
+			return Lookup<TComponent>().FirstEntity();
+		}
+
+		public ReadOnlySpan<TComponent> ReadComponents<TComponent>() where TComponent : unmanaged
+		{
+			return Lookup<TComponent>().AllComponents();
+		}
+
+		public void Remove(int entityID, int storageIndex)
+		{
+			storages[storageIndex].Remove(entityID);
+		}
+
+		public void Remove<TComponent>(int entityID) where TComponent : unmanaged
+		{
+			Lookup<TComponent>().Remove(entityID);
+		}
+
+		public void Clear()
+		{
+			for (var i = 0; i < ComponentTypeIndices.Count; i += 1)
+			{
+				if (storages[i] != null)
+				{
+					storages[i].Clear();
+				}
+			}
+		}
+
+		// these methods used to implement snapshots, templates, and debugging
+
+		internal unsafe void* UntypedGet(int entityID, int componentTypeIndex)
+		{
+			return storages[componentTypeIndex].UntypedGet(entityID);
+		}
+
+		internal unsafe void Set(int entityID, int componentTypeIndex, void* component)
+		{
+			storages[componentTypeIndex].Set(entityID, component);
+		}
+
+		public void CreateMissingStorages(ComponentDepot other)
+		{
+			for (var i = 0; i < ComponentTypeIndices.Count; i += 1)
+			{
+				if (storages[i] == null && other.storages[i] != null)
+				{
+					storages[i] = other.storages[i].CreateStorage();
+				}
+			}
+		}
+
+		// this method is used to iterate components of an entity, only for use with a debug inspector
+
+#if DEBUG
+		public object Debug_Get(int entityID, int componentTypeIndex)
+		{
+			return storages[componentTypeIndex].Debug_Get(entityID);
+		}
+
+		public IEnumerable<int> Debug_GetEntityIDs(int componentTypeIndex)
+		{
+			return storages[componentTypeIndex].Debug_GetEntityIDs();
+		}
+#endif
+	}
+}

src/ComponentStorage.cs

@@ -1,142 +1,148 @@
 using System;
 using System.Collections.Generic;
-using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS;
-
-internal class ComponentStorage : IDisposable
+namespace MoonTools.ECS
 {
-	internal readonly Dictionary<Entity, int> EntityIDToStorageIndex = new Dictionary<Entity, int>(16);
-	internal readonly NativeArray Components;
-	internal readonly NativeArray<Entity> EntityIDs;
-	internal readonly TypeId TypeId;
-	internal readonly int ElementSize;
-
-	private bool IsDisposed;
-
-	public ComponentStorage(TypeId typeId, int elementSize)
+	internal abstract class ComponentStorage
 	{
-		ElementSize = elementSize;
-		Components = new NativeArray(elementSize);
-		EntityIDs = new NativeArray<Entity>();
-		TypeId = typeId;
-	}
+		internal abstract unsafe void Set(int entityID, void* component);
+		public abstract bool Remove(int entityID);
+		public abstract void Clear();
 
-	public bool Any()
-	{
-		return Components.Count > 0;
-	}
-
-	public bool Has(Entity entity)
-	{
-		return EntityIDToStorageIndex.ContainsKey(entity);
-	}
-
-	public ref T Get<T>(in Entity entity) where T : unmanaged
-	{
-		return ref Components.Get<T>(EntityIDToStorageIndex[entity]);
-	}
-
-	public ref T GetFirst<T>() where T : unmanaged
-	{
+		// used for debugging and template instantiation
+		internal abstract unsafe void* UntypedGet(int entityID);
+		// used to create correctly typed storage on snapshot
+		public abstract ComponentStorage CreateStorage();
 #if DEBUG
-		if (Components.Count == 0)
-		{
-			throw new IndexOutOfRangeException("Component storage is empty!");
-		}
+		internal abstract object Debug_Get(int entityID);
+		internal abstract IEnumerable<int> Debug_GetEntityIDs();
 #endif
-		return ref Components.Get<T>(0);
 	}
 
-	// Returns true if the entity had this component.
-	public bool Set<T>(in Entity entity, in T component) where T : unmanaged
+	internal class ComponentStorage<TComponent> : ComponentStorage where TComponent : unmanaged
 	{
-		if (EntityIDToStorageIndex.TryGetValue(entity, out var index))
+		private int nextID;
+		private readonly Dictionary<int, int> entityIDToStorageIndex = new Dictionary<int, int>(16);
+		private int[] entityIDs = new int[16];
+		private TComponent[] components = new TComponent[16];
+
+		public bool Any()
 		{
-			Components.Set(index, component);
-			return true;
+			return nextID > 0;
 		}
-		else
+
+		public ref readonly TComponent Get(int entityID)
 		{
-			EntityIDToStorageIndex[entity] = Components.Count;
-			EntityIDs.Append(entity);
-			Components.Append(component);
-			return false;
+			return ref components[entityIDToStorageIndex[entityID]];
 		}
-	}
 
-	// Returns true if the entity had this component.
-	public bool Remove(in Entity entity)
-	{
-		if (EntityIDToStorageIndex.TryGetValue(entity, out int index))
+		internal override unsafe void* UntypedGet(int entityID)
 		{
-			var lastElementIndex = Components.Count - 1;
-
-			var lastEntity = EntityIDs[lastElementIndex];
-
-			// move a component into the hole to maintain contiguous memory
-			Components.Delete(index);
-			EntityIDs.Delete(index);
-			EntityIDToStorageIndex.Remove(entity);
-
-			// update the index if it changed
-			if (lastElementIndex != index)
+			fixed (void* p = &components[entityIDToStorageIndex[entityID]])
 			{
-				EntityIDToStorageIndex[lastEntity] = index;
+				return p;
+			}
+		}
+
+		public ref readonly TComponent GetFirst()
+		{
+#if DEBUG
+			if (nextID == 0)
+			{
+				throw new IndexOutOfRangeException("Component storage is empty!");
+			}
+#endif
+			return ref components[0];
+		}
+
+		public void Set(int entityID, in TComponent component)
+		{
+			if (!entityIDToStorageIndex.ContainsKey(entityID))
+			{
+				var index = nextID;
+				nextID += 1;
+
+				if (index >= components.Length)
+				{
+					Array.Resize(ref components, components.Length * 2);
+					Array.Resize(ref entityIDs, entityIDs.Length * 2);
+				}
+
+				entityIDToStorageIndex[entityID] = index;
+				entityIDs[index] = entityID;
 			}
 
-			return true;
+			components[entityIDToStorageIndex[entityID]] = component;
 		}
 
-		return false;
-	}
-
-	public void Clear()
-	{
-		Components.Clear();
-		EntityIDs.Clear();
-		EntityIDToStorageIndex.Clear();
-	}
-
-	public Entity FirstEntity()
-	{
-#if DEBUG
-		if (EntityIDs.Count == 0)
+		internal override unsafe void Set(int entityID, void* component)
 		{
-			throw new IndexOutOfRangeException("Component storage is empty!");
+			Set(entityID, *((TComponent*) component));
 		}
+
+		// Returns true if the entity had this component.
+		public override bool Remove(int entityID)
+		{
+			if (entityIDToStorageIndex.TryGetValue(entityID, out int storageIndex))
+			{
+				entityIDToStorageIndex.Remove(entityID);
+
+				var lastElementIndex = nextID - 1;
+
+				// move a component into the hole to maintain contiguous memory
+				if (lastElementIndex != storageIndex)
+				{
+					var lastEntityID = entityIDs[lastElementIndex];
+					entityIDToStorageIndex[lastEntityID] = storageIndex;
+					components[storageIndex] = components[lastElementIndex];
+					entityIDs[storageIndex] = lastEntityID;
+				}
+
+				nextID -= 1;
+
+				return true;
+			}
+
+			return false;
+		}
+
+		public override void Clear()
+		{
+			nextID = 0;
+			entityIDToStorageIndex.Clear();
+		}
+
+		public ReadOnlySpan<TComponent> AllComponents()
+		{
+			return new ReadOnlySpan<TComponent>(components, 0, nextID);
+		}
+
+		public Entity FirstEntity()
+		{
+#if DEBUG
+			if (nextID == 0)
+			{
+				throw new IndexOutOfRangeException("Component storage is empty!");
+			}
 #endif
-		return EntityIDs[0];
-	}
+			return new Entity(entityIDs[0]);
+		}
+
+		public override ComponentStorage<TComponent> CreateStorage()
+		{
+			return new ComponentStorage<TComponent>();
+		}
 
 #if DEBUG
-	internal IEnumerable<Entity> Debug_GetEntities()
-	{
-		return EntityIDToStorageIndex.Keys;
-	}
-#endif
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
+		internal override object Debug_Get(int entityID)
 		{
-			Components.Dispose();
-			EntityIDs.Dispose();
-
-			IsDisposed = true;
+			return components[entityIDToStorageIndex[entityID]];
 		}
-	}
 
-	// ~ComponentStorage()
-	// {
-	// 	// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-	// 	Dispose(disposing: false);
-	// }
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
+		internal override IEnumerable<int> Debug_GetEntityIDs()
+		{
+			return entityIDToStorageIndex.Keys;
+		}
+#endif
 	}
 }

src/DebugSystem.cs

@@ -1,17 +1,44 @@
 // NOTE: these methods are very inefficient
 // this class should only be used in debugging contexts!!
+
 #if DEBUG
 using System;
 using System.Collections.Generic;
 
-namespace MoonTools.ECS;
-
-public abstract class DebugSystem : System
+namespace MoonTools.ECS
 {
-	protected DebugSystem(World world) : base(world) { }
+	public abstract class DebugSystem : System
+	{
+		protected DebugSystem(World world) : base(world)
+		{
+		}
 
-	protected World.ComponentTypeEnumerator Debug_GetAllComponentTypes(Entity entity) => World.Debug_GetAllComponentTypes(entity);
-	protected IEnumerable<Entity> Debug_GetEntities(Type componentType) => World.Debug_GetEntities(componentType);
-	protected IEnumerable<Type> Debug_SearchComponentType(string typeString) => World.Debug_SearchComponentType(typeString);
+		protected IEnumerable<dynamic> Debug_GetAllComponents(Entity entity)
+		{
+			foreach (var typeIndex in EntityStorage.ComponentTypeIndices(entity.ID))
+			{
+				yield return ComponentDepot.Debug_Get(entity.ID, typeIndex);
+			}
+		}
+
+		protected IEnumerable<Entity> Debug_GetEntities(Type componentType)
+		{
+			foreach (var entityID in ComponentDepot.Debug_GetEntityIDs(ComponentTypeIndices.GetIndex(componentType)))
+			{
+				yield return new Entity(entityID);
+			}
+		}
+
+		protected IEnumerable<Type> Debug_SearchComponentType(string typeString)
+		{
+			foreach (var type in ComponentTypeIndices.Types)
+			{
+				if (type.ToString().ToLower().Contains(typeString.ToLower()))
+				{
+					yield return type;
+				}
+			}
+		}
+	}
 }
 #endif

src/DynamicArray.cs

@@ -0,0 +1,40 @@
+using System;
+
+namespace MoonTools.ECS
+{
+	public class DynamicArray<T> where T : unmanaged
+	{
+		private T[] Array;
+		public int Count { get; private set; }
+
+		public Span<T> ToSpan() => new Span<T>(Array, 0, Count);
+		public ReverseSpanEnumerator<T> GetEnumerator() => new ReverseSpanEnumerator<T>(new Span<T>(Array, 0, Count));
+
+		public DynamicArray(int capacity = 16)
+		{
+			Array = new T[capacity];
+			Count = 0;
+		}
+
+		public ref T this[int i]
+		{
+			get { return ref Array[i]; }
+		}
+
+		public void Add(T item)
+		{
+			if (Count >= Array.Length)
+			{
+				global::System.Array.Resize(ref Array, Array.Length * 2);
+			}
+
+			Array[Count] = item;
+			Count += 1;
+		}
+
+		public void Clear()
+		{
+			Count = 0;
+		}
+	}
+}

src/Entity.cs

@@ -1,3 +1,49 @@
-namespace MoonTools.ECS;
+using System;
 
-public readonly record struct Entity(uint ID);
+namespace MoonTools.ECS
+{
+	public struct Entity : IEquatable<Entity>
+	{
+		public int ID { get; }
+
+		internal Entity(int id)
+		{
+			ID = id;
+		}
+
+		public override bool Equals(object? obj)
+		{
+			return obj is Entity entity && Equals(entity);
+		}
+
+		public override int GetHashCode()
+		{
+			return HashCode.Combine(ID);
+		}
+
+		public bool Equals(Entity other)
+		{
+			return ID == other.ID;
+		}
+
+		public static bool operator ==(Entity a, Entity b)
+		{
+			return a.Equals(b);
+		}
+
+		public static bool operator !=(Entity a, Entity b)
+		{
+			return !a.Equals(b);
+		}
+
+		public static implicit operator int(Entity e)
+		{
+			return e.ID;
+		}
+
+		public static implicit operator Entity(int i)
+		{
+			return new Entity(i);
+		}
+	}
+}

src/EntityComponentReader.cs

@@ -1,36 +1,112 @@
-namespace MoonTools.ECS;
+using System;
+using System.Collections.Generic;
 
-public abstract class EntityComponentReader
+namespace MoonTools.ECS
 {
-	protected readonly World World;
-	public FilterBuilder FilterBuilder => World.FilterBuilder;
-
-	protected EntityComponentReader(World world)
+	public abstract class EntityComponentReader
 	{
-		World = world;
+		internal readonly World World;
+		internal EntityStorage EntityStorage => World.EntityStorage;
+		internal ComponentDepot ComponentDepot => World.ComponentDepot;
+		internal RelationDepot RelationDepot => World.RelationDepot;
+		protected FilterBuilder FilterBuilder => new FilterBuilder(FilterStorage, ComponentTypeIndices, RelationTypeIndices);
+		internal FilterStorage FilterStorage => World.FilterStorage;
+		internal TypeIndices ComponentTypeIndices => World.ComponentTypeIndices;
+		internal TypeIndices RelationTypeIndices => World.RelationTypeIndices;
+		internal TemplateStorage TemplateStorage => World.TemplateStorage;
+		internal ComponentDepot TemplateComponentDepot => World.TemplateComponentDepot;
+
+		public EntityComponentReader(World world)
+		{
+			World = world;
+		}
+
+		protected ReadOnlySpan<TComponent> ReadComponents<TComponent>() where TComponent : unmanaged
+		{
+			return ComponentDepot.ReadComponents<TComponent>();
+		}
+
+		protected bool Has<TComponent>(in Entity entity) where TComponent : unmanaged
+		{
+			var storageIndex = ComponentTypeIndices.GetIndex<TComponent>();
+			return EntityStorage.HasComponent(entity.ID, storageIndex);
+		}
+
+		protected bool Some<TComponent>() where TComponent : unmanaged
+		{
+			return ComponentDepot.Some<TComponent>();
+		}
+
+		protected ref readonly TComponent Get<TComponent>(in Entity entity) where TComponent : unmanaged
+		{
+			return ref ComponentDepot.Get<TComponent>(entity.ID);
+		}
+
+		protected ref readonly TComponent GetSingleton<TComponent>() where TComponent : unmanaged
+		{
+			return ref ComponentDepot.GetFirst<TComponent>();
+		}
+
+		protected Entity GetSingletonEntity<TComponent>() where TComponent : unmanaged
+		{
+			return ComponentDepot.GetSingletonEntity<TComponent>();
+		}
+
+		protected ReverseSpanEnumerator<(Entity, Entity)> Relations<TRelationKind>() where TRelationKind : unmanaged
+		{
+			return RelationDepot.Relations<TRelationKind>();
+		}
+
+		protected bool Related<TRelationKind>(in Entity a, in Entity b) where TRelationKind : unmanaged
+		{
+			return RelationDepot.Related<TRelationKind>(a.ID, b.ID);
+		}
+
+		protected TRelationKind GetRelationData<TRelationKind>(in Entity a, in Entity b) where TRelationKind : unmanaged
+		{
+			return RelationDepot.Get<TRelationKind>(a, b);
+		}
+
+		// relations go A->B, so given A, will give all entities in outgoing relations of this kind.
+		protected ReverseSpanEnumerator<Entity> OutRelations<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.OutRelations<TRelationKind>(entity.ID);
+		}
+
+		protected Entity OutRelationSingleton<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.OutRelationSingleton<TRelationKind>(entity.ID);
+		}
+
+		protected bool HasOutRelation<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.HasOutRelation<TRelationKind>(entity.ID);
+		}
+
+		protected int OutRelationCount<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.OutRelationCount<TRelationKind>(entity.ID);
+		}
+
+		// Relations go A->B, so given B, will give all entities in incoming A relations of this kind.
+		protected ReverseSpanEnumerator<Entity> InRelations<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.InRelations<TRelationKind>(entity.ID);
+		}
+
+		protected Entity InRelationSingleton<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.InRelationSingleton<TRelationKind>(entity.ID);
+		}
+
+		protected bool HasInRelation<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.HasInRelation<TRelationKind>(entity.ID);
+		}
+
+		protected int InRelationCount<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			return RelationDepot.InRelationCount<TRelationKind>(entity.ID);
+		}
 	}
-
-	protected string GetTag(in Entity entity) => World.GetTag(entity);
-
-	protected bool Has<T>(in Entity Entity) where T : unmanaged => World.Has<T>(Entity);
-	protected bool Some<T>() where T : unmanaged => World.Some<T>();
-	protected ref T Get<T>(in Entity Entity) where T : unmanaged => ref World.Get<T>(Entity);
-	protected ref T GetSingleton<T>() where T : unmanaged => ref World.GetSingleton<T>();
-	protected Entity GetSingletonEntity<T>() where T : unmanaged => World.GetSingletonEntity<T>();
-
-	protected ReverseSpanEnumerator<(Entity, Entity)> Relations<T>() where T : unmanaged => World.Relations<T>();
-	protected bool Related<T>(in Entity entityA, in Entity entityB) where T : unmanaged => World.Related<T>(entityA, entityB);
-	protected T GetRelationData<T>(in Entity entityA, in Entity entityB) where T : unmanaged => World.GetRelationData<T>(entityA, entityB);
-
-	protected ReverseSpanEnumerator<Entity> OutRelations<T>(in Entity entity) where T : unmanaged => World.OutRelations<T>(entity);
-	protected Entity OutRelationSingleton<T>(in Entity entity) where T : unmanaged => World.OutRelationSingleton<T>(entity);
-	protected bool HasOutRelation<T>(in Entity entity) where T : unmanaged => World.HasOutRelation<T>(entity);
-	protected int OutRelationCount<T>(in Entity entity) where T : unmanaged => World.OutRelationCount<T>(entity);
-	protected Entity NthOutRelation<T>(in Entity entity, int n) where T : unmanaged => World.NthOutRelation<T>(entity, n);
-
-	protected ReverseSpanEnumerator<Entity> InRelations<T>(in Entity entity) where T : unmanaged => World.InRelations<T>(entity);
-	protected Entity InRelationSingleton<T>(in Entity entity) where T : unmanaged => World.InRelationSingleton<T>(entity);
-	protected bool HasInRelation<T>(in Entity entity) where T : unmanaged => World.HasInRelation<T>(entity);
-	protected int InRelationCount<T>(in Entity entity) where T : unmanaged => World.InRelationCount<T>(entity);
-	protected Entity NthInRelation<T>(in Entity entity, int n) where T : unmanaged => World.NthInRelation<T>(entity, n);
 }

src/EntityStorage.cs

@@ -0,0 +1,117 @@
+using System.Collections.Generic;
+
+namespace MoonTools.ECS
+{
+	internal class EntityStorage
+	{
+		private int nextID = 0;
+		// FIXME: why is this duplicated?
+		private readonly Stack<int> availableIDs = new Stack<int>();
+		// FIXME: this is only needed in debug mode
+		private readonly HashSet<int> availableIDHash = new HashSet<int>();
+
+		private Dictionary<int, HashSet<int>> EntityToComponentTypeIndices = new Dictionary<int, HashSet<int>>();
+		private Dictionary<int, HashSet<int>> EntityToRelationTypeIndices = new Dictionary<int, HashSet<int>>();
+
+		public int Count => nextID - availableIDs.Count;
+
+		public Entity Create()
+		{
+			var entity = new Entity(NextID());
+			EntityToComponentTypeIndices.TryAdd(entity.ID, new HashSet<int>());
+			EntityToRelationTypeIndices.TryAdd(entity.ID, new HashSet<int>());
+			return entity;
+		}
+
+		public bool Exists(in Entity entity)
+		{
+			return Taken(entity.ID);
+		}
+
+		public void Destroy(in Entity entity)
+		{
+			EntityToComponentTypeIndices[entity.ID].Clear();
+			EntityToRelationTypeIndices[entity.ID].Clear();
+			Release(entity.ID);
+		}
+
+		// Returns true if the component is new.
+		public bool SetComponent(int entityID, int componentTypeIndex)
+		{
+			return EntityToComponentTypeIndices[entityID].Add(componentTypeIndex);
+		}
+
+		public bool HasComponent(int entityID, int componentTypeIndex)
+		{
+			return EntityToComponentTypeIndices[entityID].Contains(componentTypeIndex);
+		}
+
+		// Returns true if the component existed.
+		public bool RemoveComponent(int entityID, int componentTypeIndex)
+		{
+			return EntityToComponentTypeIndices[entityID].Remove(componentTypeIndex);
+		}
+
+		public void AddRelationKind(int entityID, int relationIndex)
+		{
+			EntityToRelationTypeIndices[entityID].Add(relationIndex);
+		}
+
+		public void RemoveRelation(int entityId, int relationIndex)
+		{
+			EntityToRelationTypeIndices[entityId].Remove(relationIndex);
+		}
+
+		public HashSet<int> ComponentTypeIndices(int entityID)
+		{
+			return EntityToComponentTypeIndices[entityID];
+		}
+
+		public HashSet<int> RelationTypeIndices(int entityID)
+		{
+			return EntityToRelationTypeIndices[entityID];
+		}
+
+		public void Clear()
+		{
+			nextID = 0;
+			foreach (var componentSet in EntityToComponentTypeIndices.Values)
+			{
+				componentSet.Clear();
+			}
+			foreach (var relationSet in EntityToRelationTypeIndices.Values)
+			{
+				relationSet.Clear();
+			}
+			availableIDs.Clear();
+			availableIDHash.Clear();
+		}
+
+		private int NextID()
+		{
+			if (availableIDs.Count > 0)
+			{
+				var id = availableIDs.Pop();
+				availableIDHash.Remove(id);
+				return id;
+			}
+			else
+			{
+				var id = nextID;
+				nextID += 1;
+				return id;
+			}
+		}
+
+		private bool Taken(int id)
+		{
+			return !availableIDHash.Contains(id) && id < nextID;
+		}
+
+		private void Release(int id)
+		{
+			availableIDs.Push(id);
+			availableIDHash.Add(id);
+		}
+	}
+}

src/Enumerators/ReverseSpanEnumerator.cs

@@ -1,35 +1,36 @@
 using System;
 using System.Runtime.CompilerServices;
 
-namespace MoonTools.ECS;
-
-public ref struct ReverseSpanEnumerator<T>
+namespace MoonTools.ECS
 {
-	private ReadOnlySpan<T> Span;
-	private int Index;
-
-	public ReverseSpanEnumerator<T> GetEnumerator() => this;
-
-	public T Current => Span[Index];
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	public bool MoveNext()
+	public ref struct ReverseSpanEnumerator<T>
 	{
-		if (Index > 0)
+		private ReadOnlySpan<T> Span;
+		private int index;
+
+		public ReverseSpanEnumerator<T> GetEnumerator() => this;
+
+		public T Current => Span[index];
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public bool MoveNext()
 		{
-			Index -= 1;
-			return true;
+			if (index > 0)
+			{
+				index -= 1;
+				return true;
+			}
+
+			return false;
 		}
 
-		return false;
-	}
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public ReverseSpanEnumerator(Span<T> span)
+		{
+			Span = span;
+			index = span.Length;
+		}
 
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	public ReverseSpanEnumerator(Span<T> span)
-	{
-		Span = span;
-		Index = span.Length;
+		public static ReverseSpanEnumerator<T> Empty => new ReverseSpanEnumerator<T>();
 	}
-
-	public static ReverseSpanEnumerator<T> Empty => new ReverseSpanEnumerator<T>();
 }

src/Filter.cs

@@ -1,123 +1,32 @@
 using System;
-using MoonTools.ECS.Collections;
+using System.Collections.Generic;
 
-namespace MoonTools.ECS;
-
-public class Filter
+namespace MoonTools.ECS
 {
-	private World World;
-	internal FilterSignature Signature;
-
-	internal IndexableSet<Entity> EntitySet = new IndexableSet<Entity>();
-
-	private bool IsDisposed;
-
-	public ReverseSpanEnumerator<Entity> Entities => EntitySet.GetEnumerator();
-
-	public bool Empty => EntitySet.Count == 0;
-	public int Count => EntitySet.Count;
-
-	// WARNING: this WILL crash if the index is out of range!
-	public Entity NthEntity(int index) => EntitySet[index];
-
-	// WARNING: this WILL crash if the filter is empty!
-	public Entity RandomEntity => EntitySet[RandomManager.Next(EntitySet.Count)];
-	public RandomEntityEnumerator EntitiesInRandomOrder => new RandomEntityEnumerator(this);
-
-	internal Filter(World world, FilterSignature signature)
+	public class Filter
 	{
-		World = world;
-		Signature = signature;
-	}
+		internal FilterSignature Signature;
+		private FilterStorage FilterStorage;
 
-	public void DestroyAllEntities()
-	{
-		foreach (var entity in EntitySet)
-		{
-			World.Destroy(entity);
-		}
-	}
-
-	internal void Check(Entity entity)
-	{
-		foreach (var type in Signature.Included)
-		{
-			if (!World.Has(entity, type))
-			{
-				EntitySet.Remove(entity);
-				return;
-			}
+		internal Filter(
+			FilterStorage filterStorage,
+			HashSet<int> included,
+			HashSet<int> excluded,
+			HashSet<int> inRelations,
+			HashSet<int> outRelations
+		) {
+			FilterStorage = filterStorage;
+			Signature = new FilterSignature(included, excluded, inRelations, outRelations);
 		}
 
-		foreach (var type in Signature.Excluded)
-		{
-			if (World.Has(entity, type))
-			{
-				EntitySet.Remove(entity);
-				return;
-			}
-		}
+		public ReverseSpanEnumerator<Entity> Entities => FilterStorage.FilterEntities(Signature);
+		public LinearCongruentialEnumerator EntitiesInRandomOrder => FilterStorage.FilterEntitiesRandom(Signature);
+		public Entity RandomEntity => FilterStorage.FilterRandomEntity(Signature);
 
-		EntitySet.Add(entity);
-	}
+		public int Count => FilterStorage.FilterCount(Signature);
+		public bool Empty => Count == 0;
 
-	internal void AddEntity(in Entity entity)
-	{
-		EntitySet.Add(entity);
-	}
-
-	internal void RemoveEntity(in Entity entity)
-	{
-		EntitySet.Remove(entity);
-	}
-
-	internal void Clear()
-	{
-		EntitySet.Clear();
-	}
-
-	public ref struct RandomEntityEnumerator
-	{
-		private Filter Filter;
-		private LinearCongruentialEnumerator LinearCongruentialEnumerator;
-
-		public RandomEntityEnumerator GetEnumerator() => this;
-
-		internal RandomEntityEnumerator(Filter filter)
-		{
-			Filter = filter;
-			LinearCongruentialEnumerator =
-				RandomManager.LinearCongruentialSequence(filter.Count);
-		}
-
-		public bool MoveNext() => LinearCongruentialEnumerator.MoveNext();
-		public Entity Current => Filter.NthEntity(LinearCongruentialEnumerator.Current);
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			if (disposing)
-			{
-				EntitySet.Dispose();
-			}
-
-			IsDisposed = true;
-		}
-	}
-
-	// // TODO: override finalizer only if 'Dispose(bool disposing)' has code to free unmanaged resources
-	// ~Filter()
-	// {
-	//     // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-	//     Dispose(disposing: false);
-	// }
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
+		// WARNING: this WILL crash if the index is out of range!
+		public Entity NthEntity(int index) => FilterStorage.FilterNthEntity(Signature, index);
 	}
 }

src/FilterBuilder.cs

@@ -1,43 +1,77 @@
-using MoonTools.ECS.Collections;
+using System;
+using System.Collections.Generic;
 
 namespace MoonTools.ECS
 {
 	public struct FilterBuilder
 	{
-		World World;
-		IndexableSet<TypeId> Included;
-		IndexableSet<TypeId> Excluded;
+		private TypeIndices ComponentTypeIndices;
+		private TypeIndices RelationTypeIndices;
+		private FilterStorage FilterStorage;
+		private HashSet<int> Included;
+		private HashSet<int> Excluded;
+		private HashSet<int> InRelations;
+		private HashSet<int> OutRelations;
 
-		internal FilterBuilder(World world)
-		{
-			World = world;
-			Included = new IndexableSet<TypeId>();
-			Excluded = new IndexableSet<TypeId>();
+		internal FilterBuilder(
+			FilterStorage filterStorage,
+			TypeIndices componentTypeIndices,
+			TypeIndices relationTypeIndices
+		) {
+			FilterStorage = filterStorage;
+			ComponentTypeIndices = componentTypeIndices;
+			RelationTypeIndices = relationTypeIndices;
+			Included = new HashSet<int>();
+			Excluded = new HashSet<int>();
+			InRelations = new HashSet<int>();
+			OutRelations = new HashSet<int>();
 		}
 
-		private FilterBuilder(World world, IndexableSet<TypeId> included, IndexableSet<TypeId> excluded)
-		{
-			World = world;
+		private FilterBuilder(
+			FilterStorage filterStorage,
+			TypeIndices componentTypeIndices,
+			TypeIndices relationTypeIndices,
+			HashSet<int> included,
+			HashSet<int> excluded,
+			HashSet<int> inRelations,
+			HashSet<int> outRelations
+		) {
+			FilterStorage = filterStorage;
+			ComponentTypeIndices = componentTypeIndices;
+			RelationTypeIndices = relationTypeIndices;
 			Included = included;
 			Excluded = excluded;
+			InRelations = inRelations;
+			OutRelations = outRelations;
 		}
 
-		public FilterBuilder Include<T>() where T : unmanaged
+		public FilterBuilder Include<TComponent>() where TComponent : unmanaged
 		{
-			Included.Add(World.GetComponentTypeId<T>());
-			return new FilterBuilder(World, Included, Excluded);
+			Included.Add(ComponentTypeIndices.GetIndex<TComponent>());
+			return this;
 		}
 
-		public FilterBuilder Exclude<T>() where T : unmanaged
+		public FilterBuilder Exclude<TComponent>() where TComponent : unmanaged
 		{
-			Excluded.Add(World.GetComponentTypeId<T>());
-			return new FilterBuilder(World, Included, Excluded);
+			Excluded.Add(ComponentTypeIndices.GetIndex<TComponent>());
+			return this;
+		}
+
+		public FilterBuilder WithInRelation<TRelation>() where TRelation : unmanaged
+		{
+			InRelations.Add(RelationTypeIndices.GetIndex<TRelation>());
+			return this;
+		}
+
+		public FilterBuilder WithOutRelation<TRelation>() where TRelation : unmanaged
+		{
+			OutRelations.Add(RelationTypeIndices.GetIndex<TRelation>());
+			return this;
 		}
 
 		public Filter Build()
 		{
-			var signature = new FilterSignature(Included, Excluded);
-			return World.GetFilter(signature);
+			return FilterStorage.CreateFilter(Included, Excluded, InRelations, OutRelations);
 		}
 	}
 }

src/FilterSignature.cs

@@ -1,69 +1,76 @@
 using System;
-using MoonTools.ECS.Collections;
+using System.Collections.Generic;
 
-namespace MoonTools.ECS;
-
-public struct FilterSignature : IEquatable<FilterSignature>
+namespace MoonTools.ECS
 {
-	public readonly IndexableSet<TypeId> Included;
-	public readonly IndexableSet<TypeId> Excluded;
-
-	public FilterSignature(IndexableSet<TypeId> included, IndexableSet<TypeId> excluded)
+	internal struct FilterSignature : IEquatable<FilterSignature>
 	{
-		Included = included;
-		Excluded = excluded;
-	}
+		public readonly HashSet<int> Included;
+		public readonly HashSet<int> Excluded;
+		public readonly HashSet<int> InRelations;
+		public readonly HashSet<int> OutRelations;
 
-	public override bool Equals(object? obj)
-	{
-		return obj is FilterSignature signature && Equals(signature);
-	}
+		public FilterSignature(
+			HashSet<int> included,
+			HashSet<int> excluded,
+			HashSet<int> inRelations,
+			HashSet<int> outRelations
+		) {
+			Included = included;
+			Excluded = excluded;
+			InRelations = inRelations;
+			OutRelations = outRelations;
+		}
 
-	public bool Equals(FilterSignature other)
-	{
-		foreach (var included in Included)
+		public override bool Equals(object? obj)
 		{
-			if (!other.Included.Contains(included))
+			return obj is FilterSignature signature && Equals(signature);
+		}
+
+		public bool Equals(FilterSignature other)
+		{
+			return
+				Included.SetEquals(other.Included) &&
+				Excluded.SetEquals(other.Excluded) &&
+				InRelations.SetEquals(other.InRelations) &&
+				OutRelations.SetEquals(other.OutRelations);
+		}
+
+		public override int GetHashCode()
+		{
+			var hashcode = 1;
+
+			foreach (var type in Included)
 			{
-				return false;
+				hashcode = HashCode.Combine(hashcode, type);
 			}
-		}
 
-		foreach (var excluded in Excluded)
-		{
-			if (!other.Excluded.Contains(excluded))
+			foreach (var type in Excluded)
 			{
-				return false;
+				hashcode = HashCode.Combine(hashcode, type);
 			}
+
+			foreach (var type in InRelations)
+			{
+				hashcode = HashCode.Combine(hashcode, type);
+			}
+
+			foreach (var type in OutRelations)
+			{
+				hashcode = HashCode.Combine(hashcode, type);
+			}
+
+			return hashcode;
 		}
 
-		return true;
-	}
-
-	public override int GetHashCode()
-	{
-		var hashcode = 1;
-
-		foreach (var type in Included)
+		public static bool operator ==(FilterSignature left, FilterSignature right)
 		{
-			hashcode = HashCode.Combine(hashcode, type);
+			return left.Equals(right);
 		}
 
-		foreach (var type in Excluded)
+		public static bool operator !=(FilterSignature left, FilterSignature right)
 		{
-			hashcode = HashCode.Combine(hashcode, type);
+			return !(left == right);
 		}
-
-		return hashcode;
-	}
-
-	public static bool operator ==(FilterSignature left, FilterSignature right)
-	{
-		return left.Equals(right);
-	}
-
-	public static bool operator !=(FilterSignature left, FilterSignature right)
-	{
-		return !(left == right);
 	}
 }

src/FilterStorage.cs

@@ -0,0 +1,196 @@
+using System;
+using System.Collections.Generic;
+
+namespace MoonTools.ECS
+{
+	internal class FilterStorage
+	{
+		private EntityStorage EntityStorage;
+		private RelationDepot RelationDepot;
+		private TypeIndices ComponentTypeIndices;
+		private TypeIndices RelationTypeIndices;
+		private Dictionary<FilterSignature, IndexableSet<Entity>> filterSignatureToEntityIDs = new Dictionary<FilterSignature, IndexableSet<Entity>>();
+		private Dictionary<int, HashSet<FilterSignature>> componentTypeToFilterSignatures = new Dictionary<int, HashSet<FilterSignature>>();
+		private Dictionary<int, HashSet<FilterSignature>> relationTypeToFilterSignatures = new Dictionary<int, HashSet<FilterSignature>>();
+
+		public FilterStorage(
+			EntityStorage entityStorage,
+			RelationDepot relationDepot,
+			TypeIndices componentTypeIndices,
+			TypeIndices relationTypeIndices
+		) {
+			EntityStorage = entityStorage;
+			RelationDepot = relationDepot;
+			ComponentTypeIndices = componentTypeIndices;
+			RelationTypeIndices = relationTypeIndices;
+		}
+
+		public Filter CreateFilter(
+			HashSet<int> included,
+			HashSet<int> excluded,
+			HashSet<int> inRelations,
+			HashSet<int> outRelations
+		) {
+			var filterSignature = new FilterSignature(included, excluded, inRelations, outRelations);
+			if (!filterSignatureToEntityIDs.ContainsKey(filterSignature))
+			{
+				filterSignatureToEntityIDs.Add(filterSignature, new IndexableSet<Entity>());
+
+				foreach (var type in included)
+				{
+					if (!componentTypeToFilterSignatures.ContainsKey(type))
+					{
+						componentTypeToFilterSignatures.Add(type, new HashSet<FilterSignature>());
+					}
+
+					componentTypeToFilterSignatures[type].Add(filterSignature);
+				}
+
+				foreach (var type in excluded)
+				{
+					if (!componentTypeToFilterSignatures.ContainsKey(type))
+					{
+						componentTypeToFilterSignatures.Add(type, new HashSet<FilterSignature>());
+					}
+
+					componentTypeToFilterSignatures[type].Add(filterSignature);
+				}
+
+				foreach (var type in inRelations)
+				{
+					if (!relationTypeToFilterSignatures.ContainsKey(type))
+					{
+						relationTypeToFilterSignatures.Add(type, new HashSet<FilterSignature>());
+					}
+
+					relationTypeToFilterSignatures[type].Add(filterSignature);
+				}
+
+				foreach (var type in outRelations)
+				{
+					if (!relationTypeToFilterSignatures.ContainsKey(type))
+					{
+						relationTypeToFilterSignatures.Add(type, new HashSet<FilterSignature>());
+					}
+
+					relationTypeToFilterSignatures[type].Add(filterSignature);
+				}
+			}
+
+			return new Filter(this, included, excluded, inRelations, outRelations);
+		}
+
+		public ReverseSpanEnumerator<Entity> FilterEntities(FilterSignature filterSignature)
+		{
+			return filterSignatureToEntityIDs[filterSignature].GetEnumerator();
+		}
+
+		public LinearCongruentialEnumerator FilterEntitiesRandom(FilterSignature filterSignature)
+		{
+			return RandomGenerator.LinearCongruentialGenerator(FilterCount(filterSignature));
+		}
+
+		public Entity FilterNthEntity(FilterSignature filterSignature, int index)
+		{
+			return new Entity(filterSignatureToEntityIDs[filterSignature][index]);
+		}
+
+		public Entity FilterRandomEntity(FilterSignature filterSignature)
+		{
+			var randomIndex = RandomGenerator.Next(FilterCount(filterSignature));
+			return new Entity(filterSignatureToEntityIDs[filterSignature][randomIndex]);
+		}
+
+		public int FilterCount(FilterSignature filterSignature)
+		{
+			return filterSignatureToEntityIDs[filterSignature].Count;
+		}
+
+		public void CheckComponentChange(int entityID, int componentTypeIndex)
+		{
+			if (componentTypeToFilterSignatures.TryGetValue(componentTypeIndex, out var filterSignatures))
+			{
+				foreach (var filterSignature in filterSignatures)
+				{
+					CheckFilter(entityID, filterSignature);
+				}
+			}
+		}
+
+		public void CheckRelationChange(int entityID, int relationTypeIndex)
+		{
+			if (relationTypeToFilterSignatures.TryGetValue(relationTypeIndex, out var filterSignatures))
+			{
+				foreach (var filterSignature in filterSignatures)
+				{
+					CheckFilter(entityID, filterSignature);
+				}
+			}
+		}
+
+		public void Check<TComponent>(int entityID) where TComponent : unmanaged
+		{
+			CheckComponentChange(entityID, ComponentTypeIndices.GetIndex<TComponent>());
+		}
+
+		public bool CheckSatisfied(int entityID, FilterSignature filterSignature)
+		{
+			foreach (var type in filterSignature.Included)
+			{
+				if (!EntityStorage.HasComponent(entityID, type))
+				{
+					return false;
+				}
+			}
+
+			foreach (var type in filterSignature.Excluded)
+			{
+				if (EntityStorage.HasComponent(entityID, type))
+				{
+					return false;
+				}
+			}
+
+			foreach (var type in filterSignature.InRelations)
+			{
+				if (!RelationDepot.HasInRelation(entityID, type))
+				{
+					return false;
+				}
+			}
+
+			foreach (var type in filterSignature.OutRelations)
+			{
+				if (!RelationDepot.HasOutRelation(entityID, type))
+				{
+					return false;
+				}
+			}
+
+			return true;
+		}
+
+		private void CheckFilter(int entityID, FilterSignature filterSignature)
+		{
+			if (CheckSatisfied(entityID, filterSignature))
+			{
+				filterSignatureToEntityIDs[filterSignature].Remove(entityID);
+			}
+			else
+			{
+				filterSignatureToEntityIDs[filterSignature].Remove(entityID);
+			}
+		}
+
+		public void RemoveEntity(int entityID, int componentTypeIndex)
+		{
+			if (componentTypeToFilterSignatures.TryGetValue(componentTypeIndex, out var filterSignatures))
+			{
+				foreach (var filterSignature in filterSignatures)
+				{
+					filterSignatureToEntityIDs[filterSignature].Remove(entityID);
+				}
+			}
+		}
+	}
+}

src/IdAssigner.cs

@@ -1,62 +0,0 @@
-using System;
-using MoonTools.ECS.Collections;
-
-namespace MoonTools.ECS;
-
-internal class IdAssigner : IDisposable
-{
-	uint Next;
-	NativeArray<uint> AvailableIds = new NativeArray<uint>();
-
-	private bool IsDisposed;
-
-	public uint Assign()
-	{
-		if (AvailableIds.TryPop(out var id))
-		{
-			return id;
-		}
-
-		id = Next;
-		Next += 1;
-		return id;
-	}
-
-	public void Unassign(uint id)
-	{
-		AvailableIds.Append(id);
-	}
-
-	public void CopyTo(IdAssigner other)
-	{
-		AvailableIds.CopyTo(other.AvailableIds);
-		other.Next = Next;
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			if (disposing)
-			{
-				AvailableIds.Dispose();
-			}
-
-			IsDisposed = true;
-		}
-	}
-
-	// // TODO: override finalizer only if 'Dispose(bool disposing)' has code to free unmanaged resources
-	// ~IdAssigner()
-	// {
-	//     // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-	//     Dispose(disposing: false);
-	// }
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
-	}
-}

src/IndexableSet.cs

@@ -0,0 +1,110 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace MoonTools.ECS
+{
+	internal class IndexableSet<T> where T : unmanaged
+	{
+		private Dictionary<T, int> indices;
+		private T[] array;
+		public int Count { get; private set; }
+		public ReverseSpanEnumerator<T> GetEnumerator() => new ReverseSpanEnumerator<T>(new Span<T>(array, 0, Count));
+
+		public IndexableSet(int size = 32)
+		{
+			indices = new Dictionary<T, int>(size);
+			array = new T[size];
+		}
+
+		public T this[int i]
+		{
+			get { return array[i]; }
+		}
+
+		public bool Contains(T element)
+		{
+			return indices.ContainsKey(element);
+		}
+
+		public bool Add(T element)
+		{
+			if (!Contains(element))
+			{
+				indices.Add(element, Count);
+
+				if (Count >= array.Length)
+				{
+					Array.Resize(ref array, array.Length * 2);
+				}
+
+				array[Count] = element;
+				Count += 1;
+
+				return true;
+			}
+
+			return false;
+		}
+
+		public bool Remove(T element)
+		{
+			if (!Contains(element))
+			{
+				return false;
+			}
+
+			var lastElement = array[Count - 1];
+			var index = indices[element];
+			array[index] = lastElement;
+			indices[lastElement] = index;
+			Count -= 1;
+			indices.Remove(element);
+
+			return true;
+		}
+
+		public void Clear()
+		{
+			Count = 0;
+		}
+
+		public struct Enumerator
+		{
+			/// <summary>The set being enumerated.</summary>
+			private readonly IndexableSet<T> _set;
+			/// <summary>The next index to yield.</summary>
+			private int _index;
+
+			/// <summary>Initialize the enumerator.</summary>
+			/// <param name="set">The set to enumerate.</param>
+			[MethodImpl(MethodImplOptions.AggressiveInlining)]
+			internal Enumerator(IndexableSet<T> set)
+			{
+				_set = set;
+				_index = _set.Count;
+			}
+
+			/// <summary>Advances the enumerator to the next element of the span.</summary>
+			[MethodImpl(MethodImplOptions.AggressiveInlining)]
+			public bool MoveNext()
+			{
+				int index = _index - 1;
+				if (index >= 0)
+				{
+					_index = index;
+					return true;
+				}
+
+				return false;
+			}
+
+			/// <summary>Gets the element at the current position of the enumerator.</summary>
+			public T Current
+			{
+				[MethodImpl(MethodImplOptions.AggressiveInlining)]
+				get => _set[_index];
+			}
+		}
+	}
+}

src/Manipulator.cs

@@ -1,20 +0,0 @@
-namespace MoonTools.ECS;
-
-public abstract class Manipulator : EntityComponentReader
-{
-	public Manipulator(World world) : base(world)
-	{
-	}
-
-	protected Entity CreateEntity(string tag = "") => World.CreateEntity(tag);
-	protected void Tag(Entity entity, string tag) => World.Tag(entity, tag);
-	protected void Set<TComponent>(in Entity entity, in TComponent component) where TComponent : unmanaged => World.Set<TComponent>(entity, component);
-	protected void Remove<TComponent>(in Entity entity) where TComponent : unmanaged => World.Remove<TComponent>(entity);
-
-	protected void Relate<TRelationKind>(in Entity entityA, in Entity entityB, TRelationKind relationData) where TRelationKind : unmanaged => World.Relate(entityA, entityB, relationData);
-	protected void Unrelate<TRelationKind>(in Entity entityA, in Entity entityB) where TRelationKind : unmanaged => World.Unrelate<TRelationKind>(entityA, entityB);
-	protected void UnrelateAll<TRelationKind>(in Entity entity) where TRelationKind : unmanaged => World.UnrelateAll<TRelationKind>(entity);
-	protected void Destroy(in Entity entity) => World.Destroy(entity);
-
-	protected void Send<TMessage>(in TMessage message) where TMessage : unmanaged => World.Send(message);
-}

src/MessageDepot.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+
+namespace MoonTools.ECS
+{
+	internal class MessageDepot
+	{
+		private Dictionary<Type, MessageStorage> storages = new Dictionary<Type, MessageStorage>();
+
+		private MessageStorage<TMessage> Lookup<TMessage>() where TMessage : unmanaged
+		{
+			if (!storages.ContainsKey(typeof(TMessage)))
+			{
+				storages.Add(typeof(TMessage), new MessageStorage<TMessage>());
+			}
+
+			return storages[typeof(TMessage)] as MessageStorage<TMessage>;
+		}
+
+		public void Add<TMessage>(in TMessage message) where TMessage : unmanaged
+		{
+			Lookup<TMessage>().Add(message);
+		}
+
+		public void Add<TMessage>(int entityID, in TMessage message) where TMessage : unmanaged
+		{
+			Lookup<TMessage>().Add(entityID, message);
+		}
+
+		public bool Some<TMessage>() where TMessage : unmanaged
+		{
+			return Lookup<TMessage>().Some();
+		}
+
+		public ReadOnlySpan<TMessage> All<TMessage>() where TMessage : unmanaged
+		{
+			return Lookup<TMessage>().All();
+		}
+
+		public TMessage First<TMessage>() where TMessage : unmanaged
+		{
+			return Lookup<TMessage>().First();
+		}
+
+		public ReverseSpanEnumerator<TMessage> WithEntity<TMessage>(int entityID) where TMessage : unmanaged
+		{
+			return Lookup<TMessage>().WithEntity(entityID);
+		}
+
+		public ref readonly TMessage FirstWithEntity<TMessage>(int entityID) where TMessage : unmanaged
+		{
+			return ref Lookup<TMessage>().FirstWithEntity(entityID);
+		}
+
+		public bool SomeWithEntity<TMessage>(int entityID) where TMessage : unmanaged
+		{
+			return Lookup<TMessage>().SomeWithEntity(entityID);
+		}
+
+		public void Clear()
+		{
+			foreach (var storage in storages.Values)
+			{
+				storage.Clear();
+			}
+		}
+	}
+}

src/MessageStorage.cs

@@ -1,63 +1,93 @@
 using System;
-using MoonTools.ECS.Collections;
+using System.Collections.Generic;
 
-namespace MoonTools.ECS;
-
-public class MessageStorage : IDisposable
+namespace MoonTools.ECS
 {
-	private NativeArray Messages;
-
-	private bool IsDisposed;
-
-	public MessageStorage(int elementSize)
+	internal abstract class MessageStorage
 	{
-		Messages = new NativeArray(elementSize);
+		public abstract void Clear();
 	}
 
-	public void Add<T>(in T message) where T : unmanaged
+	internal class MessageStorage<TMessage> : MessageStorage where TMessage : unmanaged
 	{
-		Messages.Append(message);
-	}
+		private int count = 0;
+		private int capacity = 128;
+		private TMessage[] messages;
+		// duplicating storage here for fast iteration
+		private Dictionary<int, DynamicArray<TMessage>> entityToMessages = new Dictionary<int, DynamicArray<TMessage>>();
 
-	public bool Some()
-	{
-		return Messages.Count > 0;
-	}
-
-	public ReadOnlySpan<T> All<T>() where T : unmanaged
-	{
-		return Messages.ToSpan<T>();
-	}
-
-	public T First<T>() where T : unmanaged
-	{
-		return Messages.Get<T>(0);
-	}
-
-	public void Clear()
-	{
-		Messages.Clear();
-	}
-
-	private void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
+		public MessageStorage()
 		{
-			Messages.Dispose();
-			IsDisposed = true;
+			messages = new TMessage[capacity];
+		}
+
+		public void Add(in TMessage message)
+		{
+			if (count == capacity)
+			{
+				capacity *= 2;
+				Array.Resize(ref messages, capacity);
+			}
+
+			messages[count] = message;
+			count += 1;
+		}
+
+		public void Add(int entityID, in TMessage message)
+		{
+			if (!entityToMessages.ContainsKey(entityID))
+			{
+				entityToMessages.Add(entityID, new DynamicArray<TMessage>());
+			}
+			entityToMessages[entityID].Add(message);
+
+			Add(message);
+		}
+
+		public bool Some()
+		{
+			return count > 0;
+		}
+
+		public ReadOnlySpan<TMessage> All()
+		{
+			return new ReadOnlySpan<TMessage>(messages, 0, count);
+		}
+
+		public TMessage First()
+		{
+			return messages[0];
+		}
+
+		public ReverseSpanEnumerator<TMessage> WithEntity(int entityID)
+		{
+			if (entityToMessages.TryGetValue(entityID, out var messages))
+			{
+				return messages.GetEnumerator();
+			}
+			else
+			{
+				return ReverseSpanEnumerator<TMessage>.Empty;
+			}
+		}
+
+		public ref readonly TMessage FirstWithEntity(int entityID)
+		{
+			return ref entityToMessages[entityID][0];
+		}
+
+		public bool SomeWithEntity(int entityID)
+		{
+			return entityToMessages.ContainsKey(entityID) && entityToMessages[entityID].Count > 0;
+		}
+
+		public override void Clear()
+		{
+			count = 0;
+			foreach (var set in entityToMessages.Values)
+			{
+				set.Clear();
+			}
 		}
 	}
-
-	// ~MessageStorage()
-	// {
-	// 	// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-	// 	Dispose(disposing: false);
-	// }
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
-	}
 }

src/Random.cs

@@ -1,208 +1,72 @@
-using System;
+using System;
 using System.Runtime.CompilerServices;
 
-namespace MoonTools.ECS;
-
-/// <summary>
-/// This class implements the well equidistributed long-period linear pseudorandom number generator.
-/// Code taken from Chris Lomont: http://lomont.org/papers/2008/Lomont_PRNG_2008.pdf
-/// </summary>
-public class Random
+namespace MoonTools.ECS
 {
-	public const int STATE_BYTE_COUNT = 68; // 16 state ints + 1 index int
-
-	uint[] State = new uint[16];
-	uint Index = 0;
-	uint Seed;
-
-	/// <summary>
-	/// Initializes the RNG with an arbitrary seed.
-	/// </summary>
-	public Random()
+	internal static class RandomGenerator
 	{
-		Init((uint) Environment.TickCount);
-	}
+		private static Random random = new Random();
 
-	/// <summary>
-	/// Initializes the RNG with a given seed.
-	/// </summary>
-	public void Init(uint seed)
-	{
-		Seed = seed;
-		uint s = seed;
-		for (int i = 0; i < 16; i++)
+		private static int[] Primes =
 		{
-			s = (((s * 214013 + 2531011) >> 16) & 0x7fffffff) | 0;
-			State[i] = ~ ~s; //i ;
+			2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,1163,1171,1181,1187,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1277,1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,1381,1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,1669,1693,1697,1699,1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,1823,1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,1951,1973,1979,1987,1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,2063,2069,2081,2083,2087,2089,2099,2111,2113,2129,2131,2137,2141,2143,2153,2161,2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,2293,2297,2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,2399,2411,2417,2423,2437,2441,2447,2459,2467,2473,2477,2503,2521,2531,2539,2543,2549,2551,2557,2579,2591,2593,2609,2617,2621,2633,2647,2657,2659,2663,2671,2677,2683,2687,2689,2693,2699,2707,2711,2713,2719,2729,2731,2741,2749,2753,2767,2777,2789,2791,2797,2801,2803,2819,2833,2837,2843,2851,2857,2861,2879,2887,2897,2903,2909,2917,2927,2939,2953,2957,2963,2969,2971,2999,3001,3011,3019,3023,3037,3041,3049,3061,3067,3079,3083,3089,3109,3119,3121,3137,3163,3167,3169,3181,3187,3191,3203,3209,3217,3221,3229,3251,3253,3257,3259,3271,3299,3301,3307,3313,3319,3323,3329,3331,3343,3347,3359,3361,3371,3373,3389,3391,3407,3413,3433,3449,3457,3461,3463,3467,3469,3491,3499,3511,3517,3527,3529,3533,3539,3541,3547,3557,3559,3571,3581,3583,3593,3607,3613,3617,3623,3631,3637,3643,3659,3671,3673,3677,3691,3697,3701,3709,3719,3727,3733,3739,3761,3767,3769,3779,3793,3797,3803,3821,3823,3833,3847,3851,3853,3863,3877,3881,3889,3907,3911,3917,3919,3923,3929,3931,3943,3947,3967,3989,4001,4003,4007,4013,4019,4021,4027,4049,4051,4057,4073,4079,4091,4093,4099,4111,4127,4129,4133,4139,4153,4157,4159,4177,4201,4211,4217,4219,4229,4231,4241,4243,4253,4259,4261,4271,4273,4283,4289,4297,4327,4337,4339,4349,4357,4363,4373,4391,4397,4409,4421,4423,4441,4447,4451,4457,4463,4481,4483,4493,4507,4513,4517,4519,4523,4547,4549,4561,4567,4583,4591,4597,4603,4621,4637,4639,4643,4649,4651,4657,4663,4673,4679,4691,4703,4721,4723,4729,4733,4751,4759,4783,4787,4789,4793,4799,4801,4813,4817,4831,4861,4871,4877,4889,4903,4909,4919,4931,4933,4937,4943,4951,4957,4967,4969,4973,4987,4993,4999,5003,5009,5011,5021,5023,5039,5051,5059,5077,5081,5087,5099,5101,5107,5113,5119,5147,5153,5167,5171,5179,5189,5197,5209,5227,5231,5233,5237,5261,5273,5279,5281,5297,5303,5309,5323,5333,5347,5351,5381,5387,5393,5399,5407,5413,5417,5419,5431,5437,5441,5443,5449,5471,5477,5479,5483,5501,5503,5507,5519,5521,5527,5531,5557,5563,5569,5573,5581,5591,5623,5639,5641,5647,5651,5653,5657,5659,5669,5683,5689,5693,5701,5711,5717,5737,5741,5743,5749,5779,5783,5791,5801,5807,5813,5821,5827,5839,5843,5849,5851,5857,5861,5867,5869,5879,5881,5897,5903,5923,5927,5939,5953,5981,5987,6007,6011,6029,6037,6043,6047,6053,6067,6073,6079,6089,6091,6101,6113,6121,6131,6133,6143,6151,6163,6173,6197,6199,6203,6211,6217,6221,6229,6247,6257,6263,6269,6271,6277,6287,6299,6301,6311,6317,6323,6329,6337,6343,6353,6359,6361,6367,6373,6379,6389,6397,6421,6427,6449,6451,6469,6473,6481,6491,6521,6529,6547,6551,6553,6563,6569,6571,6577,6581,6599,6607,6619,6637,6653,6659,6661,6673,6679,6689,6691,6701,6703,6709,6719,6733,6737,6761,6763,6779,6781,6791,6793,6803,6823,6827,6829,6833,6841,6857,6863,6869,6871,6883,6899,6907,6911,6917,6947,6949,6959,6961,6967,6971,6977,6983,6991,6997,7001,7013,7019,7027,7039,7043,7057,7069,7079,7103,7109,7121,7127,7129,7151,7159,7177,7187,7193,7207,7211,7213,7219,7229,7237,7243,7247,7253,7283,7297,7307,7309,7321,7331,7333,7349,7351,7369,7393,7411,7417,7433,7451,7457,7459,7477,7481,7487,7489,7499,7507,7517,7523,7529,7537,7541,7547,7549,7559,7561,7573,7577,7583,7589,7591,7603,7607,7621,7639,7643,7649,7669,7673,7681,7687,7691,7699,7703,7717,7723,7727,7741,7753,7757,7759,7789,7793,7817,7823,7829,7841,7853,7867,7873,7877,7879,7883,7901,7907,7919
+		};
+
+		public static int Next(int maxValue)
+		{
+			return random.Next(maxValue);
 		}
-		Index = 0;
-	}
 
-	/// <summary>
-	/// Returns the seed that was used to initialize the RNG.
-	/// </summary>
-	public uint GetSeed()
-	{
-		return Seed;
-	}
-
-	/// <summary>
-	/// Returns the entire state of the RNG as a string.
-	/// </summary>
-	public string PrintState()
-	{
-		var s = "";
-		for (var i = 0; i < 16; i += 1)
+		/// <summary>
+		/// A psuedorandom nonrepeating sequence of integers from 0 to n.
+		/// </summary>
+		public static LinearCongruentialEnumerator LinearCongruentialGenerator(int n)
 		{
-			s += State[i];
-		}
-		s += Index;
-		return s;
-	}
-
-	/// <summary>
-	/// Saves the entire state of the RNG to a Span.
-	/// </summary>
-	/// <param name="bytes">Must be a span of at least STATE_BYTE_COUNT bytes.</param>
-	/// <exception cref="ArgumentException">Thrown if the byte span is too short.</exception>
-	public unsafe void SaveState(Span<byte> bytes)
-	{
-#if DEBUG
-		if (bytes.Length < STATE_BYTE_COUNT)
-		{
-			throw new ArgumentException("Byte span too short!");
-		}
-#endif
-
-		fixed (byte* ptr = bytes)
-		{
-			var offset = 0;
-			for (var i = 0; i < 16; i += 1)
+			var x = Primes[random.Next(Primes.Length - 1)];
+			while (x % n == 0)
 			{
-				Unsafe.Write(ptr + offset, State[i]);
-				offset += 4;
+				// not coprime, try again
+				x = Primes[random.Next(Primes.Length - 1)];
 			}
 
-			Unsafe.Write(ptr + offset, Index);
+			return new LinearCongruentialEnumerator(random.Next(n), x, n);
 		}
 	}
 
-	/// <summary>
-	/// Loads the entire state of the RNG from a Span.
-	/// </summary>
-	/// <param name="bytes">Must be a span of at least STATE_BYTE_COUNT bytes.</param>
-	/// <exception cref="ArgumentException">Thrown if the byte span is too short.</exception>
-	public unsafe void LoadState(Span<byte> bytes)
+	public struct LinearCongruentialEnumerator
 	{
-#if DEBUG
-		if (bytes.Length < STATE_BYTE_COUNT)
+		private readonly int start;
+		private readonly int count;
+		private readonly int prime;
+		private int current;
+
+		public LinearCongruentialEnumerator GetEnumerator() => this;
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		internal LinearCongruentialEnumerator(int start, int prime, int count)
 		{
-			throw new ArgumentException("Byte span too short!");
+			current = start;
+			this.start = start;
+			this.prime = prime;
+			this.count = count;
 		}
-#endif
 
-		fixed (byte* ptr = bytes)
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		public bool MoveNext()
 		{
-			var offset = 0;
-
-			for (var i = 0; i < 16; i += 1)
+			current += 1;
+			if (current < start + count)
 			{
-				State[i] = Unsafe.Read<uint>(ptr + offset);
-				offset += 4;
+				return true;
 			}
 
-			Index = Unsafe.Read<uint>(ptr + offset);
+			return false;
 		}
-	}
 
-	private uint NextInternal()
-	{
-		uint a, b, c, d;
-		a = State[Index];
-		c = State[(Index+13)&15];
-		b = a^c^(a<<16)^(c<<15);
-		c = State[(Index+9)&15];
-		c ^= (c>>11);
-		a = State[Index] = b^c;
-		d = (uint) (a ^((a<<5)&0xDA442D24UL));
-		Index = (Index + 15)&15;
-		a = State[Index];
-		State[Index] = a^b^d^(a<<2)^(b<<18)^(c<<28);
-		return State[Index];
-	}
-
-	/// <summary>
-	/// Returns a non-negative signed integer.
-	/// </summary>
-	public int Next()
-	{
-		return (int) (NextInternal() >>> 1); // unsigned bitshift right to get rid of signed bit
-	}
-
-	/// <summary>
-	/// Returns a non-negative signed integer less than max.
-	/// </summary>
-	public int Next(int max)
-	{
-		return (int) (((double) Next()) * max / int.MaxValue);
-	}
-
-	/// <summary>
-	/// Returns a signed integer greater than or equal to min and less than max.
-	/// </summary>
-	public int Next(int min, int max)
-	{
-		var diff = max - min;
-		var next = Next(diff);
-		return min + next;
-	}
-
-	/// <summary>
-	/// Returns a non-negative signed 64 bit integer.
-	/// </summary>
-	public long NextInt64()
-	{
-		long next = NextInternal();
-		next <<= 32;
-		next |= NextInternal();
-		next >>>= 1;
-		return next;
-	}
-
-	/// <summary>
-	/// Returns a non-negative signed 64 bit integer less than max.
-	/// </summary>
-	public long NextInt64(long max)
-	{
-		var next = NextInt64();
-		return (long) (((double) next) * max / long.MaxValue);
-	}
-
-	/// <summary>
-	/// Returns a non-negative signed 64 bit integer greater than or equal to min and less than max.
-	/// </summary>
-	public long NextInt64(long min, long max)
-	{
-		var diff = max - min;
-		var next = NextInt64(diff);
-		return min + next;
-	}
-
-	/// <summary>
-	/// Returns a single-precision floating point value between 0 and 1.
-	/// </summary>
-	public float NextSingle()
-	{
-		var n = NextInternal();
-		return ((float) n) / uint.MaxValue;
-	}
-
-	/// <summary>
-	/// Returns a double-precision floating point value between 0 and 1.
-	/// </summary>
-	public double NextDouble()
-	{
-		var n = NextInternal();
-		return ((double) n) / uint.MaxValue;
+		public int Current
+		{
+			[MethodImpl(MethodImplOptions.AggressiveInlining)]
+			get => (current * prime) % count;
+		}
 	}
 }

src/RandomManager.cs

@@ -1,81 +0,0 @@
-using System.Runtime.CompilerServices;
-
-namespace MoonTools.ECS;
-
-public static class RandomManager
-{
-	private static Random Random = new Random();
-
-	private static int[] Primes =
-	{
-		2,3,5,7,11,13,17,19,23,29,31,37,41,43,47,53,59,61,67,71,73,79,83,89,97,101,103,107,109,113,127,131,137,139,149,151,157,163,167,173,179,181,191,193,197,199,211,223,227,229,233,239,241,251,257,263,269,271,277,281,283,293,307,311,313,317,331,337,347,349,353,359,367,373,379,383,389,397,401,409,419,421,431,433,439,443,449,457,461,463,467,479,487,491,499,503,509,521,523,541,547,557,563,569,571,577,587,593,599,601,607,613,617,619,631,641,643,647,653,659,661,673,677,683,691,701,709,719,727,733,739,743,751,757,761,769,773,787,797,809,811,821,823,827,829,839,853,857,859,863,877,881,883,887,907,911,919,929,937,941,947,953,967,971,977,983,991,997,1009,1013,1019,1021,1031,1033,1039,1049,1051,1061,1063,1069,1087,1091,1093,1097,1103,1109,1117,1123,1129,1151,1153,1163,1171,1181,1187,1193,1201,1213,1217,1223,1229,1231,1237,1249,1259,1277,1279,1283,1289,1291,1297,1301,1303,1307,1319,1321,1327,1361,1367,1373,1381,1399,1409,1423,1427,1429,1433,1439,1447,1451,1453,1459,1471,1481,1483,1487,1489,1493,1499,1511,1523,1531,1543,1549,1553,1559,1567,1571,1579,1583,1597,1601,1607,1609,1613,1619,1621,1627,1637,1657,1663,1667,1669,1693,1697,1699,1709,1721,1723,1733,1741,1747,1753,1759,1777,1783,1787,1789,1801,1811,1823,1831,1847,1861,1867,1871,1873,1877,1879,1889,1901,1907,1913,1931,1933,1949,1951,1973,1979,1987,1993,1997,1999,2003,2011,2017,2027,2029,2039,2053,2063,2069,2081,2083,2087,2089,2099,2111,2113,2129,2131,2137,2141,2143,2153,2161,2179,2203,2207,2213,2221,2237,2239,2243,2251,2267,2269,2273,2281,2287,2293,2297,2309,2311,2333,2339,2341,2347,2351,2357,2371,2377,2381,2383,2389,2393,2399,2411,2417,2423,2437,2441,2447,2459,2467,2473,2477,2503,2521,2531,2539,2543,2549,2551,2557,2579,2591,2593,2609,2617,2621,2633,2647,2657,2659,2663,2671,2677,2683,2687,2689,2693,2699,2707,2711,2713,2719,2729,2731,2741,2749,2753,2767,2777,2789,2791,2797,2801,2803,2819,2833,2837,2843,2851,2857,2861,2879,2887,2897,2903,2909,2917,2927,2939,2953,2957,2963,2969,2971,2999,3001,3011,3019,3023,3037,3041,3049,3061,3067,3079,3083,3089,3109,3119,3121,3137,3163,3167,3169,3181,3187,3191,3203,3209,3217,3221,3229,3251,3253,3257,3259,3271,3299,3301,3307,3313,3319,3323,3329,3331,3343,3347,3359,3361,3371,3373,3389,3391,3407,3413,3433,3449,3457,3461,3463,3467,3469,3491,3499,3511,3517,3527,3529,3533,3539,3541,3547,3557,3559,3571,3581,3583,3593,3607,3613,3617,3623,3631,3637,3643,3659,3671,3673,3677,3691,3697,3701,3709,3719,3727,3733,3739,3761,3767,3769,3779,3793,3797,3803,3821,3823,3833,3847,3851,3853,3863,3877,3881,3889,3907,3911,3917,3919,3923,3929,3931,3943,3947,3967,3989,4001,4003,4007,4013,4019,4021,4027,4049,4051,4057,4073,4079,4091,4093,4099,4111,4127,4129,4133,4139,4153,4157,4159,4177,4201,4211,4217,4219,4229,4231,4241,4243,4253,4259,4261,4271,4273,4283,4289,4297,4327,4337,4339,4349,4357,4363,4373,4391,4397,4409,4421,4423,4441,4447,4451,4457,4463,4481,4483,4493,4507,4513,4517,4519,4523,4547,4549,4561,4567,4583,4591,4597,4603,4621,4637,4639,4643,4649,4651,4657,4663,4673,4679,4691,4703,4721,4723,4729,4733,4751,4759,4783,4787,4789,4793,4799,4801,4813,4817,4831,4861,4871,4877,4889,4903,4909,4919,4931,4933,4937,4943,4951,4957,4967,4969,4973,4987,4993,4999,5003,5009,5011,5021,5023,5039,5051,5059,5077,5081,5087,5099,5101,5107,5113,5119,5147,5153,5167,5171,5179,5189,5197,5209,5227,5231,5233,5237,5261,5273,5279,5281,5297,5303,5309,5323,5333,5347,5351,5381,5387,5393,5399,5407,5413,5417,5419,5431,5437,5441,5443,5449,5471,5477,5479,5483,5501,5503,5507,5519,5521,5527,5531,5557,5563,5569,5573,5581,5591,5623,5639,5641,5647,5651,5653,5657,5659,5669,5683,5689,5693,5701,5711,5717,5737,5741,5743,5749,5779,5783,5791,5801,5807,5813,5821,5827,5839,5843,5849,5851,5857,5861,5867,5869,5879,5881,5897,5903,5923,5927,5939,5953,5981,5987,6007,6011,6029,6037,6043,6047,6053,6067,6073,6079,6089,6091,6101,6113,6121,6131,6133,6143,6151,6163,6173,6197,6199,6203,6211,6217,6221,6229,6247,6257,6263,6269,6271,6277,6287,6299,6301,6311,6317,6323,6329,6337,6343,6353,6359,6361,6367,6373,6379,6389,6397,6421,6427,6449,6451,6469,6473,6481,6491,6521,6529,6547,6551,6553,6563,6569,6571,6577,6581,6599,6607,6619,6637,6653,6659,6661,6673,6679,6689,6691,6701,6703,6709,6719,6733,6737,6761,6763,6779,6781,6791,6793,6803,6823,6827,6829,6833,6841,6857,6863,6869,6871,6883,6899,6907,6911,6917,6947,6949,6959,6961,6967,6971,6977,6983,6991,6997,7001,7013,7019,7027,7039,7043,7057,7069,7079,7103,7109,7121,7127,7129,7151,7159,7177,7187,7193,7207,7211,7213,7219,7229,7237,7243,7247,7253,7283,7297,7307,7309,7321,7331,7333,7349,7351,7369,7393,7411,7417,7433,7451,7457,7459,7477,7481,7487,7489,7499,7507,7517,7523,7529,7537,7541,7547,7549,7559,7561,7573,7577,7583,7589,7591,7603,7607,7621,7639,7643,7649,7669,7673,7681,7687,7691,7699,7703,7717,7723,7727,7741,7753,7757,7759,7789,7793,7817,7823,7829,7841,7853,7867,7873,7877,7879,7883,7901,7907,7919
-	};
-
-	public static void SetRandom(Random random)
-	{
-		Random = random;
-	}
-
-	internal static int Next(int maxValue)
-	{
-		return Random.Next(maxValue);
-	}
-
-	/// <summary>
-	/// A psuedorandom nonrepeating sequence of integers from 0 to n.
-	/// </summary>
-	internal static LinearCongruentialEnumerator LinearCongruentialSequence(int n)
-	{
-		if (n == 0)
-		{
-			// bail out, empty enumerator
-			return new LinearCongruentialEnumerator(0, 0, 0);
-		}
-
-		var x = Primes[Random.Next(Primes.Length - 1)];
-		while (x % n == 0)
-		{
-			// not coprime, try again
-			x = Primes[Random.Next(Primes.Length - 1)];
-		}
-
-		return new LinearCongruentialEnumerator(Random.Next(n + 1), x, n);
-	}
-}
-
-public struct LinearCongruentialEnumerator
-{
-	private readonly int start;
-	private readonly int count;
-	private readonly int prime;
-	private int current;
-
-	public LinearCongruentialEnumerator GetEnumerator() => this;
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	internal LinearCongruentialEnumerator(int start, int prime, int count)
-	{
-		current = start;
-		this.start = start;
-		this.prime = prime;
-		this.count = count;
-	}
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	public bool MoveNext()
-	{
-		current += 1;
-		if (current <= start + count)
-		{
-			return true;
-		}
-
-		return false;
-	}
-
-	public int Current
-	{
-		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		get => (current * prime) % count;
-	}
-}

src/RelationDepot.cs

@@ -0,0 +1,168 @@
+using System;
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace MoonTools.ECS
+{
+	internal class RelationDepot
+	{
+		private TypeIndices RelationTypeIndices;
+		private RelationStorage[] storages = new RelationStorage[256];
+
+		public RelationDepot(TypeIndices relationTypeIndices)
+		{
+			RelationTypeIndices = relationTypeIndices;
+		}
+
+		private void Register<TRelationKind>(int index) where TRelationKind : unmanaged
+		{
+			if (index >= storages.Length)
+			{
+				Array.Resize(ref storages, storages.Length * 2);
+			}
+
+			storages[index] = new RelationStorage<TRelationKind>();
+		}
+
+		[MethodImpl(MethodImplOptions.AggressiveInlining)]
+		private RelationStorage<TRelationKind> Lookup<TRelationKind>() where TRelationKind : unmanaged
+		{
+			var storageIndex = RelationTypeIndices.GetIndex<TRelationKind>();
+			// TODO: is there some way to avoid this null check?
+			if (storages[storageIndex] == null)
+			{
+				Register<TRelationKind>(storageIndex);
+			}
+			return (RelationStorage<TRelationKind>) storages[storageIndex];
+		}
+
+		public void Set<TRelationKind>(in Entity entityA, in Entity entityB, TRelationKind relationData) where TRelationKind : unmanaged
+		{
+			Lookup<TRelationKind>().Set(entityA, entityB, relationData);
+		}
+
+		public TRelationKind Get<TRelationKind>(in Entity entityA, in Entity entityB) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().Get(entityA, entityB);
+		}
+
+		public (bool, bool) Remove<TRelationKind>(in Entity entityA, in Entity entityB) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().Remove(entityA, entityB);
+		}
+
+		public void UnrelateAll<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			Lookup<TRelationKind>().UnrelateAll(entityID);
+		}
+
+		public ReverseSpanEnumerator<(Entity, Entity)> Relations<TRelationKind>() where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().All();
+		}
+
+		public bool Related<TRelationKind>(int idA, int idB) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().Has((idA, idB));
+		}
+
+		public ReverseSpanEnumerator<Entity> OutRelations<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().OutRelations(entityID);
+		}
+
+		public Entity OutRelationSingleton<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().OutFirst(entityID);
+		}
+
+		public int OutRelationCount<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().OutRelationCount(entityID);
+		}
+
+		public bool HasOutRelation<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().HasOutRelation(entityID);
+		}
+
+		public bool HasOutRelation(int entityID, int typeIndex)
+		{
+			return storages[typeIndex].HasOutRelation(entityID);
+		}
+
+		public ReverseSpanEnumerator<Entity> InRelations<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().InRelations(entityID);
+		}
+
+		public Entity InRelationSingleton<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().InFirst(entityID);
+		}
+
+		public bool HasInRelation<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().HasInRelation(entityID);
+		}
+
+		public bool HasInRelation(int entityID, int typeIndex)
+		{
+			return storages[typeIndex].HasInRelation(entityID);
+		}
+
+		public int InRelationCount<TRelationKind>(int entityID) where TRelationKind : unmanaged
+		{
+			return Lookup<TRelationKind>().InRelationCount(entityID);
+		}
+
+		// untyped methods used for destroying and snapshots
+
+		public unsafe void Set(int entityA, int entityB, int relationTypeIndex, void* relationData)
+		{
+			storages[relationTypeIndex].Set(entityA, entityB, relationData);
+		}
+
+		public int GetStorageIndex(int relationTypeIndex, int entityA, int entityB)
+		{
+			return storages[relationTypeIndex].GetStorageIndex(entityA, entityB);
+		}
+
+		public unsafe void* Get(int relationTypeIndex, int relationStorageIndex)
+		{
+			return storages[relationTypeIndex].Get(relationStorageIndex);
+		}
+
+		public void UnrelateAll(int entityID, int relationTypeIndex)
+		{
+			storages[relationTypeIndex].UnrelateAll(entityID);
+		}
+
+		public ReverseSpanEnumerator<Entity> OutRelations(int entityID, int relationTypeIndex)
+		{
+			return storages[relationTypeIndex].OutRelations(entityID);
+		}
+
+		public void Clear()
+		{
+			for (var i = 0; i < RelationTypeIndices.Count; i += 1)
+			{
+				if (storages[i] != null)
+				{
+					storages[i].Clear();
+				}
+			}
+		}
+
+		public void CreateMissingStorages(RelationDepot other)
+		{
+			for (var i = 0; i < RelationTypeIndices.Count; i += 1)
+			{
+				if (storages[i] == null && other.storages[i] != null)
+				{
+					storages[i] = other.storages[i].CreateStorage();
+				}
+			}
+		}
+	}
+}

src/RelationStorage.cs

@@ -1,286 +1,278 @@
 using System;
 using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS;
-
-// TODO: implement this entire class with NativeMemory equivalents, can just memcpy for snapshots
-internal class RelationStorage
+namespace MoonTools.ECS
 {
-	internal NativeArray Relations;
-	internal NativeArray RelationDatas;
-	internal int ElementSize;
-	internal Dictionary<(Entity, Entity), int> Indices = new Dictionary<(Entity, Entity), int>(16);
-	internal Dictionary<Entity, IndexableSet<Entity>> OutRelationSets = new Dictionary<Entity, IndexableSet<Entity>>(16);
-	internal Dictionary<Entity, IndexableSet<Entity>> InRelationSets = new Dictionary<Entity, IndexableSet<Entity>>(16);
-	private Stack<IndexableSet<Entity>> ListPool = new Stack<IndexableSet<Entity>>();
-
-	private bool IsDisposed;
-
-	public RelationStorage(int relationDataSize)
+	internal abstract class RelationStorage
 	{
-		ElementSize = relationDataSize;
-		Relations = new NativeArray(Unsafe.SizeOf<(Entity, Entity)>());
-		RelationDatas = new NativeArray(relationDataSize);
+		public abstract bool HasInRelation(int entityID);
+		public abstract bool HasOutRelation(int entityID);
+		public abstract unsafe void Set(int entityA, int entityB, void* relationData);
+		public abstract int GetStorageIndex(int entityA, int entityB);
+		public abstract unsafe void* Get(int relationStorageIndex);
+		public abstract void UnrelateAll(int entityID);
+		public abstract ReverseSpanEnumerator<Entity> OutRelations(int entityID);
+		public abstract RelationStorage CreateStorage();
+		public abstract void Clear();
 	}
 
-	public ReverseSpanEnumerator<(Entity, Entity)> All()
+	// Relation is the two entities, A related to B.
+	// TRelation is the data attached to the relation.
+	internal class RelationStorage<TRelation> : RelationStorage where TRelation : unmanaged
 	{
-		return new ReverseSpanEnumerator<(Entity, Entity)>(Relations.ToSpan<(Entity, Entity)>());
-	}
+		private int count = 0;
+		private Dictionary<(Entity, Entity), int> indices = new Dictionary<(Entity, Entity), int>(16);
+		private (Entity, Entity)[] relations = new (Entity, Entity)[16];
+		private TRelation[] relationDatas = new TRelation[16];
+		private Dictionary<int, IndexableSet<Entity>> outRelations = new Dictionary<int, IndexableSet<Entity>>(16);
+		private Dictionary<int, IndexableSet<Entity>> inRelations = new Dictionary<int, IndexableSet<Entity>>(16);
+		private Stack<IndexableSet<Entity>> listPool = new Stack<IndexableSet<Entity>>();
 
-	public unsafe void Set<T>(in Entity entityA, in Entity entityB, in T relationData) where T : unmanaged
-	{
-		var relation = (entityA, entityB);
-
-		if (Indices.TryGetValue(relation, out var index))
+		public ReverseSpanEnumerator<(Entity, Entity)> All()
 		{
-			RelationDatas.Set(index, relationData);
-			return;
+			return new ReverseSpanEnumerator<(Entity, Entity)>(new Span<(Entity, Entity)>(relations, 0, count));
 		}
 
-		if (!OutRelationSets.ContainsKey(entityA))
+		public void Set(in Entity entityA, in Entity entityB, TRelation relationData)
 		{
-			OutRelationSets[entityA] = AcquireHashSetFromPool();
-		}
-		OutRelationSets[entityA].Add(entityB);
+			var relation = (entityA, entityB);
 
-		if (!InRelationSets.ContainsKey(entityB))
+			if (indices.TryGetValue(relation, out var index))
+			{
+				relationDatas[index] = relationData;
+				return;
+			}
+
+			var idA = entityA.ID;
+			var idB = entityB.ID;
+
+			if (!outRelations.ContainsKey(idA))
+			{
+				outRelations[idA] = AcquireHashSetFromPool();
+			}
+			outRelations[idA].Add(idB);
+
+			if (!inRelations.ContainsKey(idB))
+			{
+				inRelations[idB] = AcquireHashSetFromPool();
+			}
+			inRelations[idB].Add(idA);
+
+			if (count >= relationDatas.Length)
+			{
+				Array.Resize(ref relations, relations.Length * 2);
+				Array.Resize(ref relationDatas, relationDatas.Length * 2);
+			}
+
+			relations[count] = relation;
+			relationDatas[count] = relationData;
+			indices.Add(relation, count);
+			count += 1;
+		}
+
+		public TRelation Get(in Entity entityA, in Entity entityB)
 		{
-			InRelationSets[entityB] = AcquireHashSetFromPool();
+			return relationDatas[indices[(entityA, entityB)]];
 		}
-		InRelationSets[entityB].Add(entityA);
 
-		Relations.Append(relation);
-		RelationDatas.Append(relationData);
-		Indices.Add(relation, Relations.Count - 1);
-	}
-
-	public ref T Get<T>(in Entity entityA, in Entity entityB) where T : unmanaged
-	{
-		var relationIndex = Indices[(entityA, entityB)];
-		return ref RelationDatas.Get<T>(relationIndex);
-	}
-
-	public bool Has(Entity entityA, Entity entityB)
-	{
-		return Indices.ContainsKey((entityA, entityB));
-	}
-
-	public ReverseSpanEnumerator<Entity> OutRelations(Entity Entity)
-	{
-		if (OutRelationSets.TryGetValue(Entity, out var entityOutRelations))
+		public bool Has((Entity, Entity) relation)
 		{
-			return entityOutRelations.GetEnumerator();
+			return indices.ContainsKey(relation);
 		}
-		else
+
+		public override ReverseSpanEnumerator<Entity> OutRelations(int entityID)
 		{
-			return ReverseSpanEnumerator<Entity>.Empty;
+			if (outRelations.TryGetValue(entityID, out var entityOutRelations))
+			{
+				return entityOutRelations.GetEnumerator();
+			}
+			else
+			{
+				return ReverseSpanEnumerator<Entity>.Empty;
+			}
 		}
-	}
 
-	public Entity OutFirst(Entity Entity)
-	{
-		return OutNth(Entity, 0);
-	}
-
-	public Entity OutNth(Entity Entity, int n)
-	{
+		public Entity OutFirst(int entityID)
+		{
 #if DEBUG
-		if (!OutRelationSets.ContainsKey(Entity) || OutRelationSets[Entity].Count == 0)
-		{
-			throw new KeyNotFoundException("No out relations to this entity!");
-		}
+			if (!outRelations.ContainsKey(entityID) || outRelations[entityID].Count == 0)
+			{
+				throw new KeyNotFoundException("No out relations to this entity!");
+			}
 #endif
-		return OutRelationSets[Entity][n];
-	}
-
-	public bool HasOutRelation(Entity Entity)
-	{
-		return OutRelationSets.ContainsKey(Entity) && OutRelationSets[Entity].Count > 0;
-	}
-
-	public int OutRelationCount(Entity Entity)
-	{
-		return OutRelationSets.TryGetValue(Entity, out var entityOutRelations) ? entityOutRelations.Count : 0;
-	}
-
-	public ReverseSpanEnumerator<Entity> InRelations(Entity Entity)
-	{
-		if (InRelationSets.TryGetValue(Entity, out var entityInRelations))
-		{
-			return entityInRelations.GetEnumerator();
+			return outRelations[entityID][0];
 		}
-		else
+
+		public override bool HasOutRelation(int entityID)
 		{
-			return ReverseSpanEnumerator<Entity>.Empty;
+			return outRelations.ContainsKey(entityID) && outRelations[entityID].Count > 0;
 		}
-	}
 
-	public Entity InFirst(Entity Entity)
-	{
-		return InNth(Entity, 0);
-	}
+		public int OutRelationCount(int entityID)
+		{
+			return outRelations.TryGetValue(entityID, out var entityOutRelations) ? entityOutRelations.Count : 0;
+		}
 
-	public Entity InNth(Entity Entity, int n)
-	{
+		public ReverseSpanEnumerator<Entity> InRelations(int entityID)
+		{
+			if (inRelations.TryGetValue(entityID, out var entityInRelations))
+			{
+				return entityInRelations.GetEnumerator();
+			}
+			else
+			{
+				return ReverseSpanEnumerator<Entity>.Empty;
+			}
+		}
+
+		public Entity InFirst(int entityID)
+		{
 #if DEBUG
-		if (!InRelationSets.ContainsKey(Entity) || InRelationSets[Entity].Count == 0)
-		{
-			throw new KeyNotFoundException("No in relations to this entity!");
-		}
+			if (!inRelations.ContainsKey(entityID) || inRelations[entityID].Count == 0)
+			{
+				throw new KeyNotFoundException("No out relations to this entity!");
+			}
 #endif
 
-		return InRelationSets[Entity][n];
-	}
+			return inRelations[entityID][0];
+		}
 
-	public bool HasInRelation(Entity Entity)
-	{
-		return InRelationSets.ContainsKey(Entity) && InRelationSets[Entity].Count > 0;
-	}
-
-	public int InRelationCount(Entity Entity)
-	{
-		return InRelationSets.TryGetValue(Entity, out var entityInRelations) ? entityInRelations.Count : 0;
-	}
-
-	public (bool, bool) Remove(in Entity entityA, in Entity entityB)
-	{
-		var aEmpty = false;
-		var bEmpty = false;
-		var relation = (entityA, entityB);
-
-		if (OutRelationSets.TryGetValue(entityA, out var entityOutRelations))
+		public override bool HasInRelation(int entityID)
 		{
-			entityOutRelations.Remove(entityB);
-			if (OutRelationSets[entityA].Count == 0)
+			return inRelations.ContainsKey(entityID) && inRelations[entityID].Count > 0;
+		}
+
+		public int InRelationCount(int entityID)
+		{
+			return inRelations.TryGetValue(entityID, out var entityInRelations) ? entityInRelations.Count : 0;
+		}
+
+		public (bool, bool) Remove(in Entity entityA, in Entity entityB)
+		{
+			var aEmpty = false;
+			var bEmpty = false;
+			var relation = (entityA, entityB);
+
+			if (outRelations.TryGetValue(entityA.ID, out var entityOutRelations))
 			{
-				aEmpty = true;
-			}
-		}
-
-		if (InRelationSets.TryGetValue(entityB, out var entityInRelations))
-		{
-			entityInRelations.Remove(entityA);
-			if (InRelationSets[entityB].Count == 0)
-			{
-				bEmpty = true;
-			}
-		}
-
-		if (Indices.TryGetValue(relation, out var index))
-		{
-			var lastElementIndex = Relations.Count - 1;
-
-			// move an element into the hole
-			if (index != lastElementIndex)
-			{
-				var lastRelation = Relations.Get<(Entity, Entity)>(lastElementIndex);
-				Indices[lastRelation] = index;
-			}
-
-			RelationDatas.Delete(index);
-			Relations.Delete(index);
-
-			Indices.Remove(relation);
-		}
-
-		return (aEmpty, bEmpty);
-	}
-
-	public void RemoveEntity(in Entity entity)
-	{
-		if (OutRelationSets.TryGetValue(entity, out var entityOutRelations))
-		{
-			foreach (var entityB in entityOutRelations)
-			{
-				Remove(entity, entityB);
-			}
-
-			ReturnHashSetToPool(entityOutRelations);
-			OutRelationSets.Remove(entity);
-		}
-
-		if (InRelationSets.TryGetValue(entity, out var entityInRelations))
-		{
-			foreach (var entityA in entityInRelations)
-			{
-				Remove(entityA, entity);
-			}
-
-			ReturnHashSetToPool(entityInRelations);
-			InRelationSets.Remove(entity);
-		}
-	}
-
-	internal IndexableSet<Entity> AcquireHashSetFromPool()
-	{
-		if (ListPool.Count == 0)
-		{
-			ListPool.Push(new IndexableSet<Entity>());
-		}
-
-		return ListPool.Pop();
-	}
-
-	private void ReturnHashSetToPool(IndexableSet<Entity> hashSet)
-	{
-		hashSet.Clear();
-		ListPool.Push(hashSet);
-	}
-
-	public void Clear()
-	{
-		Indices.Clear();
-
-		foreach (var set in InRelationSets.Values)
-		{
-			ReturnHashSetToPool(set);
-		}
-		InRelationSets.Clear();
-
-		foreach (var set in OutRelationSets.Values)
-		{
-			ReturnHashSetToPool(set);
-		}
-		OutRelationSets.Clear();
-
-		Relations.Clear();
-		RelationDatas.Clear();
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			Clear();
-
-			if (disposing)
-			{
-				foreach (var set in ListPool)
+				entityOutRelations.Remove(entityB.ID);
+				if (outRelations[entityA.ID].Count == 0)
 				{
-					set.Dispose();
+					aEmpty = true;
+				}
+			}
+
+			if (inRelations.TryGetValue(entityB.ID, out var entityInRelations))
+			{
+				entityInRelations.Remove(entityA.ID);
+				if (inRelations[entityB.ID].Count == 0)
+				{
+					bEmpty = true;
+				}
+			}
+
+			if (indices.TryGetValue(relation, out var index))
+			{
+				var lastElementIndex = count - 1;
+
+				// move an element into the hole
+				if (index != lastElementIndex)
+				{
+					var lastRelation = relations[lastElementIndex];
+					indices[lastRelation] = index;
+					relationDatas[index] = relationDatas[lastElementIndex];
+					relations[index] = lastRelation;
 				}
 
-				Relations.Dispose();
-				RelationDatas.Dispose();
+				count -= 1;
+				indices.Remove(relation);
 			}
 
-			IsDisposed = true;
+			return (aEmpty, bEmpty);
+		}
+
+		private IndexableSet<Entity> AcquireHashSetFromPool()
+		{
+			if (listPool.Count == 0)
+			{
+				listPool.Push(new IndexableSet<Entity>());
+			}
+
+			return listPool.Pop();
+		}
+
+		private void ReturnHashSetToPool(IndexableSet<Entity> hashSet)
+		{
+			hashSet.Clear();
+			listPool.Push(hashSet);
+		}
+
+		// untyped methods used for internal implementation
+
+		public override unsafe void Set(int entityA, int entityB, void* relationData)
+		{
+			Set(entityA, entityB, *((TRelation*) relationData));
+		}
+
+		public override int GetStorageIndex(int entityA, int entityB)
+		{
+			return indices[(entityA, entityB)];
+		}
+
+		public override unsafe void* Get(int relationStorageIndex)
+		{
+			fixed (void* p = &relations[relationStorageIndex])
+			{
+				return p;
+			}
+		}
+
+		public override void UnrelateAll(int entityID)
+		{
+			if (outRelations.TryGetValue(entityID, out var entityOutRelations))
+			{
+				foreach (var entityB in entityOutRelations)
+				{
+					Remove(entityID, entityB);
+				}
+
+				ReturnHashSetToPool(entityOutRelations);
+				outRelations.Remove(entityID);
+			}
+
+			if (inRelations.TryGetValue(entityID, out var entityInRelations))
+			{
+				foreach (var entityA in entityInRelations)
+				{
+					Remove(entityA, entityID);
+				}
+
+				ReturnHashSetToPool(entityInRelations);
+				inRelations.Remove(entityID);
+			}
+		}
+
+		public override RelationStorage<TRelation> CreateStorage()
+		{
+			return new RelationStorage<TRelation>();
+		}
+
+		public override void Clear()
+		{
+			count = 0;
+			indices.Clear();
+
+			foreach (var set in inRelations.Values)
+			{
+				ReturnHashSetToPool(set);
+			}
+			inRelations.Clear();
+
+			foreach (var set in outRelations.Values)
+			{
+				ReturnHashSetToPool(set);
+			}
+			outRelations.Clear();
 		}
 	}
-
-	// ~RelationStorage()
-	// {
-	// 	// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-	// 	Dispose(disposing: false);
-	// }
-
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
-	}
 }

src/Renderer.cs

@@ -1,6 +1,7 @@
-namespace MoonTools.ECS;
-
-public abstract class Renderer : EntityComponentReader
+namespace MoonTools.ECS
 {
-	public Renderer(World world) : base(world) { }
+	public abstract class Renderer : EntityComponentReader
+	{
+		public Renderer(World world) : base(world) { }
+	}
 }

src/Snapshot.cs

@@ -1,378 +1,122 @@
-using System;
+using System;
 using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS;
-
-// TODO: we should implement a NativeDictionary that can be memcopied
-public class Snapshot : IDisposable
+namespace MoonTools.ECS
 {
-	private List<ComponentSnapshot> ComponentSnapshots = new List<ComponentSnapshot>();
-
-	// FIXME: we could just have a filter ID
-	private Dictionary<FilterSignature, List<Entity>> Filters = new Dictionary<FilterSignature, List<Entity>>();
-
-	private List<RelationSnapshot> RelationSnapshots = new List<RelationSnapshot>();
-
-	private List<IndexableSet<TypeId>> EntityRelationIndex =
-		new List<IndexableSet<TypeId>>();
-
-	private List<IndexableSet<TypeId>> EntityComponentIndex =
-		new List<IndexableSet<TypeId>>();
-
-	private List<string> EntityTags = new List<string>();
-
-	private IdAssigner EntityIdAssigner = new IdAssigner();
-
-	private bool IsDisposed;
-
-	public void Restore(World world)
+	public class Snapshot
 	{
-		// restore id assigner state
-		EntityIdAssigner.CopyTo(world.EntityIdAssigner);
+		private World World;
+		private Filter? Filter;
 
-		// restore filter states
-		// this could be sped up if we figured out a direct IndexableSet copy
-		foreach (var (signature, entityList) in Filters)
+		private EntityStorage SnapshotEntityStorage;
+		private ComponentDepot SnapshotComponentDepot;
+		private RelationDepot SnapshotRelationDepot;
+
+		private List<int> SnapshotToWorldID = new List<int>();
+		private Dictionary<int, int> WorldToSnapshotID = new Dictionary<int, int>();
+
+		internal Snapshot(World world)
 		{
-			var filter = world.FilterIndex[signature];
+			World = world;
+			SnapshotEntityStorage = new EntityStorage();
+			SnapshotComponentDepot = new ComponentDepot(World.ComponentTypeIndices);
+			SnapshotRelationDepot = new RelationDepot(World.RelationTypeIndices);
+		}
 
-			filter.Clear();
+		public unsafe void Take(Filter filter)
+		{
+			Clear();
+			Filter = filter;
+			SnapshotComponentDepot.CreateMissingStorages(World.ComponentDepot);
+			SnapshotRelationDepot.CreateMissingStorages(World.RelationDepot);
 
-			foreach (var entity in entityList)
+			foreach (var worldEntity in filter.Entities)
 			{
-				filter.AddEntity(entity);
-			}
-		}
+				var snapshotEntity = SnapshotEntityStorage.Create();
+				WorldToSnapshotID.Add(worldEntity.ID, snapshotEntity.ID);
 
-		// clear all component storages in case any were created after snapshot
-		// FIXME: this can be eliminated via component discovery
-		foreach (var componentStorage in world.ComponentIndex)
-		{
-			componentStorage.Clear();
-		}
-
-		// clear all relation storages in case any were created after snapshot
-		// FIXME: this can be eliminated via component discovery
-		foreach (var relationStorage in world.RelationIndex)
-		{
-			relationStorage.Clear();
-		}
-
-		for (var i = 0; i < ComponentSnapshots.Count; i += 1)
-		{
-			var componentStorage = world.ComponentIndex[i];
-			ComponentSnapshots[i].Restore(componentStorage);
-		}
-
-		// restore relation state
-		for (var i = 0; i < RelationSnapshots.Count; i += 1)
-		{
-			var relationStorage = world.RelationIndex[i];
-			RelationSnapshots[i].Restore(relationStorage);
-		}
-
-		// restore entity relation index state
-		// FIXME: arghhhh this is so slow
-
-		foreach (var relationTypeSet in world.EntityRelationIndex)
-		{
-			relationTypeSet.Clear();
-		}
-
-		for (var i = 0; i < EntityRelationIndex.Count; i += 1)
-		{
-			var relationTypeSet = EntityRelationIndex[i];
-
-			foreach (var typeId in relationTypeSet)
-			{
-				world.EntityRelationIndex[i].Add(typeId);
-			}
-		}
-
-		// restore entity component index state
-		// FIXME: arrghghhh this is so slow
-
-		foreach (var componentTypeSet in world.EntityComponentIndex)
-		{
-			componentTypeSet.Clear();
-		}
-
-		for (var i = 0; i < EntityComponentIndex.Count; i += 1)
-		{
-			var componentTypeSet = EntityComponentIndex[i];
-
-			foreach (var typeId in componentTypeSet)
-			{
-				world.EntityComponentIndex[i].Add(typeId);
-			}
-		}
-
-		// restore entity tags
-		for (var i = 0; i < EntityTags.Count; i += 1)
-		{
-			world.EntityTags[i] = EntityTags[i];
-		}
-	}
-
-	public void Take(World world)
-	{
-		// copy id assigner state
-		world.EntityIdAssigner.CopyTo(EntityIdAssigner);
-
-		// copy filter states
-		foreach (var (_, filter) in world.FilterIndex)
-		{
-			TakeFilterSnapshot(filter);
-		}
-
-		// copy components
-		for (var i = ComponentSnapshots.Count; i < world.ComponentIndex.Count; i += 1)
-		{
-			ComponentSnapshots.Add(new ComponentSnapshot(world.ComponentIndex[i].ElementSize));
-		}
-
-		for (var i = 0; i < world.ComponentIndex.Count; i += 1)
-		{
-			ComponentSnapshots[i].Take(world.ComponentIndex[i]);
-		}
-
-		// copy relations
-		for (var i = RelationSnapshots.Count; i < world.RelationIndex.Count; i += 1)
-		{
-			RelationSnapshots.Add(new RelationSnapshot(world.RelationIndex[i].ElementSize));
-		}
-
-		for (var i = 0; i < world.RelationIndex.Count; i += 1)
-		{
-			RelationSnapshots[i].Take(world.RelationIndex[i]);
-		}
-
-		// fill in missing index structures
-
-		for (var i = EntityComponentIndex.Count; i < world.EntityComponentIndex.Count; i += 1)
-		{
-			EntityComponentIndex.Add(new IndexableSet<TypeId>());
-		}
-
-		for (var i = EntityRelationIndex.Count; i < world.EntityRelationIndex.Count; i += 1)
-		{
-			EntityRelationIndex.Add(new IndexableSet<TypeId>());
-		}
-
-		// copy entity relation index
-		// FIXME: arghhhh this is so slow
-		for (var i = 0; i < world.EntityRelationIndex.Count; i += 1)
-		{
-			EntityRelationIndex[i].Clear();
-
-			foreach (var typeId in world.EntityRelationIndex[i])
-			{
-				EntityRelationIndex[i].Add(typeId);
-			}
-		}
-
-		// copy entity component index
-		// FIXME: arghhhh this is so slow
-		for (var i = 0; i < world.EntityComponentIndex.Count; i += 1)
-		{
-			EntityComponentIndex[i].Clear();
-
-			foreach (var typeId in world.EntityComponentIndex[i])
-			{
-				EntityComponentIndex[i].Add(typeId);
-			}
-		}
-
-		// copy entity tags
-		EntityTags.Clear();
-		foreach (var s in world.EntityTags)
-		{
-			EntityTags.Add(s);
-		}
-	}
-
-	private void TakeFilterSnapshot(Filter filter)
-	{
-		if (!Filters.TryGetValue(filter.Signature, out var entities))
-		{
-			entities = new List<Entity>();
-			Filters.Add(filter.Signature, entities);
-		}
-
-		entities.Clear();
-
-		foreach (var entity in filter.EntitySet.AsSpan())
-		{
-			entities.Add(entity);
-		}
-	}
-
-	private class ComponentSnapshot : IDisposable
-	{
-		private readonly NativeArray Components;
-		private readonly NativeArray<Entity> EntityIDs;
-
-		private bool IsDisposed;
-
-		public ComponentSnapshot(int elementSize)
-		{
-			Components = new NativeArray(elementSize);
-			EntityIDs = new NativeArray<Entity>();
-		}
-
-		public void Take(ComponentStorage componentStorage)
-		{
-			componentStorage.Components.CopyAllTo(Components);
-			componentStorage.EntityIDs.CopyTo(EntityIDs);
-		}
-
-		public void Restore(ComponentStorage componentStorage)
-		{
-			Components.CopyAllTo(componentStorage.Components);
-			EntityIDs.CopyTo(componentStorage.EntityIDs);
-
-			componentStorage.EntityIDToStorageIndex.Clear();
-			for (int i = 0; i < EntityIDs.Count; i += 1)
-			{
-				var entityID = EntityIDs[i];
-				componentStorage.EntityIDToStorageIndex[entityID] = i;
-			}
-		}
-
-		protected virtual void Dispose(bool disposing)
-		{
-			if (!IsDisposed)
-			{
-				if (disposing)
+				foreach (var componentTypeIndex in World.EntityStorage.ComponentTypeIndices(worldEntity.ID))
 				{
-					Components.Dispose();
-					EntityIDs.Dispose();
+					SnapshotEntityStorage.SetComponent(snapshotEntity.ID, componentTypeIndex);
+					SnapshotComponentDepot.Set(snapshotEntity.ID, componentTypeIndex, World.ComponentDepot.UntypedGet(worldEntity.ID, componentTypeIndex));
 				}
-
-				IsDisposed = true;
 			}
-		}
 
-		public void Dispose()
-		{
-			// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-			Dispose(disposing: true);
-			GC.SuppressFinalize(this);
-		}
-	}
-
-	private class RelationSnapshot : IDisposable
-	{
-		private NativeArray Relations;
-		private NativeArray RelationDatas;
-
-		private bool IsDisposed;
-
-		public RelationSnapshot(int elementSize)
-		{
-			Relations = new NativeArray(Unsafe.SizeOf<(Entity, Entity)>());
-			RelationDatas = new NativeArray(elementSize);
-		}
-
-		public void Take(RelationStorage relationStorage)
-		{
-			relationStorage.Relations.CopyAllTo(Relations);
-			relationStorage.RelationDatas.CopyAllTo(RelationDatas);
-		}
-
-		public void Restore(RelationStorage relationStorage)
-		{
-			relationStorage.Clear();
-
-			Relations.CopyAllTo(relationStorage.Relations);
-			RelationDatas.CopyAllTo(relationStorage.RelationDatas);
-
-			for (int index = 0; index < Relations.Count; index += 1)
+			foreach (var worldEntity in filter.Entities)
 			{
-				var relation = Relations.Get<(Entity, Entity)>(index);
-				relationStorage.Indices[relation] = index;
+				var snapshotEntityID = WorldToSnapshotID[worldEntity.ID];
 
-				relationStorage.Indices[relation] = index;
-
-				if (!relationStorage.OutRelationSets.ContainsKey(relation.Item1))
+				foreach (var relationTypeIndex in World.EntityStorage.RelationTypeIndices(worldEntity.ID))
 				{
-					relationStorage.OutRelationSets[relation.Item1] =
-						relationStorage.AcquireHashSetFromPool();
+					SnapshotEntityStorage.AddRelationKind(snapshotEntityID, relationTypeIndex);
+
+					foreach (var otherEntityID in World.RelationDepot.OutRelations(worldEntity.ID, relationTypeIndex))
+					{
+#if DEBUG
+						if (!World.FilterStorage.CheckSatisfied(otherEntityID, Filter.Signature))
+						{
+							throw new InvalidOperationException($"Snapshot entity {worldEntity.ID} is related to non-snapshot entity {otherEntityID}!");
+						}
+#endif
+						var relationStorageIndex = World.RelationDepot.GetStorageIndex(relationTypeIndex, worldEntity, otherEntityID);
+						var otherSnapshotID = WorldToSnapshotID[otherEntityID];
+						SnapshotEntityStorage.AddRelationKind(otherSnapshotID, relationTypeIndex);
+						SnapshotRelationDepot.Set(snapshotEntityID, otherSnapshotID, relationTypeIndex, World.RelationDepot.Get(relationTypeIndex, relationStorageIndex));
+					}
 				}
-
-				relationStorage.OutRelationSets[relation.Item1].Add(relation.Item2);
-
-				if (!relationStorage.InRelationSets.ContainsKey(relation.Item2))
-				{
-					relationStorage.InRelationSets[relation.Item2] =
-						relationStorage.AcquireHashSetFromPool();
-				}
-
-				relationStorage.InRelationSets[relation.Item2].Add(relation.Item1);
 			}
 		}
 
-		protected virtual void Dispose(bool disposing)
+		public unsafe void Restore()
 		{
-			if (!IsDisposed)
+			if (Filter == null)
 			{
-				if (disposing)
-				{
-					Relations.Dispose();
-					RelationDatas.Dispose();
-				}
-
-				IsDisposed = true;
+				return;
 			}
-		}
 
-		public void Dispose()
-		{
-			// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-			Dispose(disposing: true);
-			GC.SuppressFinalize(this);
-		}
-	}
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			if (disposing)
+			foreach (var entity in Filter.Entities)
 			{
-				foreach (var componentSnapshot in ComponentSnapshots)
-				{
-					componentSnapshot.Dispose();
-				}
-
-				foreach (var relationSnapshot in RelationSnapshots)
-				{
-					relationSnapshot.Dispose();
-				}
-
-				foreach (var componentSet in EntityComponentIndex)
-				{
-					componentSet.Dispose();
-				}
-
-				foreach (var relationSet in EntityRelationIndex)
-				{
-					relationSet.Dispose();
-				}
-
-				EntityIdAssigner.Dispose();
+				World.Destroy(entity);
 			}
 
-			IsDisposed = true;
-		}
-	}
+			for (var i = 0; i < SnapshotEntityStorage.Count; i += 1)
+			{
+				var entity = World.CreateEntity();
+				SnapshotToWorldID.Add(entity.ID);
 
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
+				foreach (var componentTypeIndex in SnapshotEntityStorage.ComponentTypeIndices(i))
+				{
+					World.EntityStorage.SetComponent(entity.ID, componentTypeIndex);
+					World.FilterStorage.CheckComponentChange(entity.ID, componentTypeIndex);
+					World.ComponentDepot.Set(entity.ID, componentTypeIndex, SnapshotComponentDepot.UntypedGet(i, componentTypeIndex));
+				}
+			}
+
+			for (var i = 0; i < SnapshotEntityStorage.Count; i += 1)
+			{
+				var worldID = SnapshotToWorldID[i];
+
+				foreach (var relationTypeIndex in SnapshotEntityStorage.RelationTypeIndices(i))
+				{
+					World.EntityStorage.AddRelationKind(worldID, relationTypeIndex);
+
+					foreach (var otherEntityID in SnapshotRelationDepot.OutRelations(i, relationTypeIndex))
+					{
+						var relationStorageIndex = SnapshotRelationDepot.GetStorageIndex(relationTypeIndex, i, otherEntityID);
+						var otherEntityWorldID = SnapshotToWorldID[otherEntityID];
+						World.RelationDepot.Set(worldID, otherEntityWorldID, relationTypeIndex, SnapshotRelationDepot.Get(relationTypeIndex, relationStorageIndex));
+					}
+				}
+			}
+		}
+
+		private void Clear()
+		{
+			SnapshotEntityStorage.Clear();
+			SnapshotComponentDepot.Clear();
+			SnapshotRelationDepot.Clear();
+			SnapshotToWorldID.Clear();
+			WorldToSnapshotID.Clear();
+		}
 	}
 }

src/System.cs

@@ -1,15 +1,102 @@
 using System;
+using System.Collections.Generic;
 
-namespace MoonTools.ECS;
-
-public abstract class System : Manipulator
+namespace MoonTools.ECS
 {
-	protected System(World world) : base(world) { }
+	public abstract class System : EntityComponentReader
+	{
+		internal MessageDepot MessageDepot => World.MessageDepot;
 
-	public abstract void Update(TimeSpan delta);
+		public System(World world) : base(world) { }
 
-	protected ReadOnlySpan<T> ReadMessages<T>() where T : unmanaged => World.ReadMessages<T>();
-	protected T ReadMessage<T>() where T : unmanaged => World.ReadMessage<T>();
-	protected bool SomeMessage<T>() where T : unmanaged => World.SomeMessage<T>();
-	protected void Send<T>(T message) where T : unmanaged => World.Send(message);
+		public abstract void Update(TimeSpan delta);
+
+		protected Entity CreateEntity() => World.CreateEntity();
+
+		protected void Set<TComponent>(in Entity entity, in TComponent component) where TComponent : unmanaged => World.Set<TComponent>(entity, component);
+
+		protected void Remove<TComponent>(in Entity entity) where TComponent : unmanaged
+		{
+			if (EntityStorage.RemoveComponent(entity.ID, ComponentTypeIndices.GetIndex<TComponent>()))
+			{
+				ComponentDepot.Remove<TComponent>(entity.ID);
+				FilterStorage.Check<TComponent>(entity.ID);
+			}
+		}
+
+		protected void Set<TComponent>(in Template template, in TComponent component) where TComponent : unmanaged => World.Set<TComponent>(template, component);
+
+		protected Entity Instantiate(in Template template) => World.Instantiate(template);
+
+		protected ReadOnlySpan<TMessage> ReadMessages<TMessage>() where TMessage : unmanaged
+		{
+			return MessageDepot.All<TMessage>();
+		}
+
+		protected TMessage ReadMessage<TMessage>() where TMessage : unmanaged
+		{
+			return MessageDepot.First<TMessage>();
+		}
+
+		protected bool SomeMessage<TMessage>() where TMessage : unmanaged
+		{
+			return MessageDepot.Some<TMessage>();
+		}
+
+		protected ReverseSpanEnumerator<TMessage> ReadMessagesWithEntity<TMessage>(in Entity entity) where TMessage : unmanaged
+		{
+			return MessageDepot.WithEntity<TMessage>(entity.ID);
+		}
+
+		protected ref readonly TMessage ReadMessageWithEntity<TMessage>(in Entity entity) where TMessage : unmanaged
+		{
+			return ref MessageDepot.FirstWithEntity<TMessage>(entity.ID);
+		}
+
+		protected bool SomeMessageWithEntity<TMessage>(in Entity entity) where TMessage : unmanaged
+		{
+			return MessageDepot.SomeWithEntity<TMessage>(entity.ID);
+		}
+
+		protected void Send<TMessage>(in TMessage message) where TMessage : unmanaged
+		{
+			MessageDepot.Add(message);
+		}
+
+		protected void Send<TMessage>(in Entity entity, in TMessage message) where TMessage : unmanaged
+		{
+			MessageDepot.Add(entity.ID, message);
+		}
+
+		protected void Relate<TRelationKind>(in Entity entityA, in Entity entityB, TRelationKind relationData) where TRelationKind : unmanaged
+		{
+			RelationDepot.Set(entityA, entityB, relationData);
+			var relationTypeIndex = RelationTypeIndices.GetIndex<TRelationKind>();
+			EntityStorage.AddRelationKind(entityA.ID, relationTypeIndex);
+			EntityStorage.AddRelationKind(entityB.ID, relationTypeIndex);
+		}
+
+		protected void Unrelate<TRelationKind>(in Entity entityA, in Entity entityB) where TRelationKind : unmanaged
+		{
+			var (aEmpty, bEmpty) = RelationDepot.Remove<TRelationKind>(entityA, entityB);
+
+			if (aEmpty)
+			{
+				EntityStorage.RemoveRelation(entityA.ID, RelationTypeIndices.GetIndex<TRelationKind>());
+			}
+
+			if (bEmpty)
+			{
+				EntityStorage.RemoveRelation(entityB.ID, RelationTypeIndices.GetIndex<TRelationKind>());
+			}
+		}
+
+		protected void UnrelateAll<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
+		{
+			RelationDepot.UnrelateAll<TRelationKind>(entity.ID);
+			EntityStorage.RemoveRelation(entity.ID, RelationTypeIndices.GetIndex<TRelationKind>());
+		}
+
+		protected void Destroy(in Entity entity) => World.Destroy(entity);
+	}
 }

src/Template.cs

@@ -0,0 +1,12 @@
+namespace MoonTools.ECS
+{
+	public struct Template
+	{
+		public int ID { get; }
+
+		internal Template(int id)
+		{
+			ID = id;
+		}
+	}
+}

src/TemplateStorage.cs

@@ -0,0 +1,34 @@
+using System.Collections.Generic;
+
+namespace MoonTools.ECS
+{
+	public class TemplateStorage
+	{
+		private int nextID = 0;
+
+		private Dictionary<int, HashSet<int>> TemplateToComponentTypeIndices = new Dictionary<int, HashSet<int>>();
+
+		public Template Create()
+		{
+			TemplateToComponentTypeIndices.Add(nextID, new HashSet<int>());
+			return new Template(NextID());
+		}
+
+		public bool SetComponent(int templateID, int componentTypeIndex)
+		{
+			return TemplateToComponentTypeIndices[templateID].Add(componentTypeIndex);
+		}
+
+		public HashSet<int> ComponentTypeIndices(int templateID)
+		{
+			return TemplateToComponentTypeIndices[templateID];
+		}
+
+		private int NextID()
+		{
+			var id = nextID;
+			nextID += 1;
+			return id;
+		}
+	}
+}

src/TypeId.cs

@@ -1,82 +0,0 @@
-using System;
-using System.Runtime.CompilerServices;
-
-namespace MoonTools.ECS;
-
-public readonly record struct TypeId(uint Value) : IComparable<TypeId>
-{
-	public int CompareTo(TypeId other)
-	{
-		return Value.CompareTo(other.Value);
-	}
-
-	public static implicit operator int(TypeId typeId)
-	{
-		return (int) typeId.Value;
-	}
-}
-
-internal class ComponentTypeIdAssigner
-{
-	protected static ushort Counter;
-}
-
-internal class ComponentTypeIdAssigner<T> : ComponentTypeIdAssigner
-{
-	public static readonly ushort Id;
-	public static readonly int Size;
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	static ComponentTypeIdAssigner()
-	{
-		Id = Counter++;
-		Size = Unsafe.SizeOf<T>();
-
-		World.ComponentTypeElementSizes.Add(Size);
-
-		#if DEBUG
-		World.ComponentTypeToId[typeof(T)] = new TypeId(Id);
-		World.ComponentTypeIdToType.Add(typeof(T));
-		#endif
-	}
-}
-
-internal class RelationTypeIdAssigner
-{
-	protected static ushort Counter;
-}
-
-internal class RelationTypeIdAssigner<T> : RelationTypeIdAssigner
-{
-	public static readonly ushort Id;
-	public static readonly int Size;
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	static RelationTypeIdAssigner()
-	{
-		Id = Counter++;
-		Size = Unsafe.SizeOf<T>();
-
-		World.RelationTypeElementSizes.Add(Size);
-	}
-}
-
-internal class MessageTypeIdAssigner
-{
-	protected static ushort Counter;
-}
-
-internal class MessageTypeIdAssigner<T> : MessageTypeIdAssigner
-{
-	public static readonly ushort Id;
-	public static readonly int Size;
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	static MessageTypeIdAssigner()
-	{
-		Id = Counter++;
-		Size = Unsafe.SizeOf<T>();
-
-		World.MessageTypeElementSizes.Add(Size);
-	}
-}

src/TypeIndices.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Collections.Generic;
+
+namespace MoonTools.ECS
+{
+	public class TypeIndices
+	{
+		Dictionary<Type, int> TypeToIndex = new Dictionary<Type, int>();
+		int nextID = 0;
+		public int Count => TypeToIndex.Count;
+
+		public int GetIndex<T>() where T : unmanaged
+		{
+			if (!TypeToIndex.ContainsKey(typeof(T)))
+			{
+				TypeToIndex.Add(typeof(T), nextID);
+				nextID += 1;
+			}
+
+			return TypeToIndex[typeof(T)];
+		}
+
+		public int GetIndex(Type type)
+		{
+			return TypeToIndex[type];
+		}
+
+
+#if DEBUG
+		public Dictionary<Type, int>.KeyCollection Types => TypeToIndex.Keys;
+#endif
+	}
+}

src/World.cs

@@ -1,506 +1,108 @@
 using System;
-using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-using MoonTools.ECS.Collections;
 
-#if DEBUG
-using System.Reflection;
-#endif
-
-namespace MoonTools.ECS;
-
-public class World : IDisposable
+namespace MoonTools.ECS
 {
+	public class World
+	{
+		internal readonly TypeIndices ComponentTypeIndices = new TypeIndices();
+		internal readonly TypeIndices RelationTypeIndices = new TypeIndices();
+		internal readonly EntityStorage EntityStorage = new EntityStorage();
+		internal readonly ComponentDepot ComponentDepot;
+		internal readonly MessageDepot MessageDepot = new MessageDepot();
+		internal readonly RelationDepot RelationDepot;
+		internal readonly FilterStorage FilterStorage;
+		public FilterBuilder FilterBuilder => new FilterBuilder(FilterStorage, ComponentTypeIndices, RelationTypeIndices);
+
+		internal readonly TemplateStorage TemplateStorage = new TemplateStorage();
+		internal readonly ComponentDepot TemplateComponentDepot;
+
+		public World()
+		{
+			ComponentDepot = new ComponentDepot(ComponentTypeIndices);
+			RelationDepot = new RelationDepot(RelationTypeIndices);
+			FilterStorage = new FilterStorage(EntityStorage, RelationDepot, ComponentTypeIndices, RelationTypeIndices);
+			TemplateComponentDepot = new ComponentDepot(ComponentTypeIndices);
+		}
+
+		public Entity CreateEntity()
+		{
+			return EntityStorage.Create();
+		}
+
+		public void Set<TComponent>(Entity entity, in TComponent component) where TComponent : unmanaged
+		{
 #if DEBUG
-	// TODO: is there a smarter way to do this?
-	internal static Dictionary<Type, TypeId> ComponentTypeToId = new Dictionary<Type, TypeId>();
-	internal static List<Type> ComponentTypeIdToType = new List<Type>();
+			// check for use after destroy
+			if (!EntityStorage.Exists(entity))
+			{
+				throw new InvalidOperationException("This entity is not valid!");
+			}
 #endif
-
-	internal static List<int> ComponentTypeElementSizes = new List<int>();
-	internal static List<int> RelationTypeElementSizes = new List<int>();
-	internal static List<int> MessageTypeElementSizes = new List<int>();
-
-	// Filters
-	internal readonly Dictionary<FilterSignature, Filter> FilterIndex = new Dictionary<FilterSignature, Filter>();
-	private readonly List<List<Filter>> ComponentTypeToFilter = new List<List<Filter>>();
-
-	// TODO: can we make the tag an native array of chars at some point?
-	internal List<string> EntityTags = new List<string>();
-
-	// Relation Storages
-	internal List<RelationStorage> RelationIndex = new List<RelationStorage>();
-	internal List<IndexableSet<TypeId>> EntityRelationIndex = new List<IndexableSet<TypeId>>();
-
-	// Message Storages
-	private List<MessageStorage> MessageIndex = new List<MessageStorage>();
-
-	public FilterBuilder FilterBuilder => new FilterBuilder(this);
-
-	internal readonly List<ComponentStorage> ComponentIndex = new List<ComponentStorage>();
-	internal List<IndexableSet<TypeId>> EntityComponentIndex = new List<IndexableSet<TypeId>>();
-
-	internal IdAssigner EntityIdAssigner = new IdAssigner();
-
-	private bool IsDisposed;
-
-	internal TypeId GetComponentTypeId<T>() where T : unmanaged
-	{
-		var typeId = new TypeId(ComponentTypeIdAssigner<T>.Id);
-		if (typeId < ComponentIndex.Count)
-		{
-			return typeId;
-		}
-
-		// add missing storages, it's possible for there to be multiples in multi-world scenarios
-		for (var i = ComponentIndex.Count; i <= typeId; i += 1)
-		{
-			var missingTypeId = new TypeId((uint) i);
-			var componentStorage = new ComponentStorage(missingTypeId, ComponentTypeElementSizes[i]);
-			ComponentIndex.Add(componentStorage);
-			ComponentTypeToFilter.Add(new List<Filter>());
-		}
-
-		return typeId;
-	}
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	private ComponentStorage GetComponentStorage<T>() where T : unmanaged
-	{
-		var typeId = GetComponentTypeId<T>();
-		return ComponentIndex[typeId];
-	}
-
-	// FILTERS
-
-	internal Filter GetFilter(FilterSignature signature)
-	{
-		if (!FilterIndex.TryGetValue(signature, out var filter))
-		{
-			filter = new Filter(this, signature);
-
-			foreach (var typeId in signature.Included)
+			if (EntityStorage.SetComponent(entity.ID, ComponentTypeIndices.GetIndex<TComponent>()))
 			{
-				ComponentTypeToFilter[(int) typeId.Value].Add(filter);
+				FilterStorage.Check<TComponent>(entity.ID);
 			}
 
-			foreach (var typeId in signature.Excluded)
+			ComponentDepot.Set<TComponent>(entity.ID, component);
+		}
+
+		public Template CreateTemplate()
+		{
+			return TemplateStorage.Create();
+		}
+
+		public void Set<TComponent>(in Template template, in TComponent component) where TComponent : unmanaged
+		{
+			var componentTypeIndex = ComponentTypeIndices.GetIndex<TComponent>();
+			TemplateStorage.SetComponent(template.ID, componentTypeIndex);
+			TemplateComponentDepot.Set(template.ID, component);
+			ComponentDepot.Register<TComponent>(componentTypeIndex);
+		}
+
+		public unsafe Entity Instantiate(in Template template)
+		{
+			var entity = EntityStorage.Create();
+
+			foreach (var componentTypeIndex in TemplateStorage.ComponentTypeIndices(template.ID))
 			{
-				ComponentTypeToFilter[(int) typeId.Value].Add(filter);
+				EntityStorage.SetComponent(entity.ID, componentTypeIndex);
+				FilterStorage.CheckComponentChange(entity.ID, componentTypeIndex);
+				ComponentDepot.Set(entity.ID, componentTypeIndex, TemplateComponentDepot.UntypedGet(template.ID, componentTypeIndex));
 			}
 
-			FilterIndex.Add(signature, filter);
+			return entity;
 		}
 
-		return filter;
-	}
-
-	// ENTITIES
-
-	public Entity CreateEntity(string tag = "")
-	{
-		var entity = new Entity(EntityIdAssigner.Assign());
-
-		if (entity.ID == EntityComponentIndex.Count)
+		public void Send<TMessage>(in TMessage message) where TMessage : unmanaged
 		{
-			EntityRelationIndex.Add(new IndexableSet<TypeId>());
-			EntityComponentIndex.Add(new IndexableSet<TypeId>());
-			EntityTags.Add(tag);
+			MessageDepot.Add(message);
 		}
 
-		return entity;
-	}
-
-	public void Tag(Entity entity, string tag)
-	{
-		EntityTags[(int) entity.ID] = tag;
-	}
-
-	public string GetTag(Entity entity)
-	{
-		return EntityTags[(int) entity.ID];
-	}
-
-	public void Destroy(in Entity entity)
-	{
-		var componentSet = EntityComponentIndex[(int) entity.ID];
-		var relationSet = EntityRelationIndex[(int) entity.ID];
-
-		// remove all components from storages
-		foreach (var componentTypeIndex in componentSet)
+		public void Destroy(in Entity entity)
 		{
-			var componentStorage = ComponentIndex[componentTypeIndex];
-			componentStorage.Remove(entity);
-
-			foreach (var filter in ComponentTypeToFilter[componentTypeIndex])
+			foreach (var componentTypeIndex in EntityStorage.ComponentTypeIndices(entity.ID))
 			{
-				filter.RemoveEntity(entity);
-			}
-		}
-
-		// remove all relations from storage
-		foreach (var relationTypeIndex in relationSet)
-		{
-			var relationStorage = RelationIndex[relationTypeIndex];
-			relationStorage.RemoveEntity(entity);
-		}
-
-		componentSet.Clear();
-		relationSet.Clear();
-
-		// recycle ID
-		EntityIdAssigner.Unassign(entity.ID);
-
-		EntityTags[(int) entity.ID] = "";
-	}
-
-	// COMPONENTS
-
-	public bool Has<T>(in Entity entity) where T : unmanaged
-	{
-		var storage = GetComponentStorage<T>();
-		return storage.Has(entity);
-	}
-
-	internal bool Has(in Entity entity, in TypeId typeId)
-	{
-		return EntityComponentIndex[(int) entity.ID].Contains(typeId);
-	}
-
-	public bool Some<T>() where T : unmanaged
-	{
-		var storage = GetComponentStorage<T>();
-		return storage.Any();
-	}
-
-	public ref T Get<T>(in Entity entity) where T : unmanaged
-	{
-		var storage = GetComponentStorage<T>();
-		return ref storage.Get<T>(entity);
-	}
-
-	public ref T GetSingleton<T>() where T : unmanaged
-	{
-		var storage = GetComponentStorage<T>();
-		return ref storage.GetFirst<T>();
-	}
-
-	public Entity GetSingletonEntity<T>() where T : unmanaged
-	{
-		var storage = GetComponentStorage<T>();
-		return storage.FirstEntity();
-	}
-
-	public void Set<T>(in Entity entity, in T component) where T : unmanaged
-	{
-		var componentStorage = GetComponentStorage<T>();
-
-		if (!componentStorage.Set(entity, component))
-		{
-			EntityComponentIndex[(int) entity.ID].Add(componentStorage.TypeId);
-
-			foreach (var filter in ComponentTypeToFilter[componentStorage.TypeId])
-			{
-				filter.Check(entity);
-			}
-		}
-	}
-
-	public void Remove<T>(in Entity entity) where T : unmanaged
-	{
-		var componentStorage = GetComponentStorage<T>();
-
-		if (componentStorage.Remove(entity))
-		{
-			EntityComponentIndex[(int) entity.ID].Remove(componentStorage.TypeId);
-
-			foreach (var filter in ComponentTypeToFilter[componentStorage.TypeId])
-			{
-				filter.Check(entity);
-			}
-		}
-	}
-
-	// RELATIONS
-
-	[MethodImpl(MethodImplOptions.AggressiveInlining)]
-	private RelationStorage GetRelationStorage<T>() where T : unmanaged
-	{
-		var typeId = new TypeId(RelationTypeIdAssigner<T>.Id);
-		if (typeId.Value < RelationIndex.Count)
-		{
-			return RelationIndex[typeId];
-		}
-
-		for (var i = RelationIndex.Count; i <= typeId; i += 1)
-		{
-			RelationIndex.Add(new RelationStorage(RelationTypeElementSizes[i]));
-		}
-
-		return RelationIndex[typeId];
-	}
-
-	public void Relate<T>(in Entity entityA, in Entity entityB, in T relation) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		relationStorage.Set(entityA, entityB, relation);
-		EntityRelationIndex[(int) entityA.ID].Add(new TypeId(RelationTypeIdAssigner<T>.Id));
-		EntityRelationIndex[(int) entityB.ID].Add(new TypeId(RelationTypeIdAssigner<T>.Id));
-	}
-
-	public void Unrelate<T>(in Entity entityA, in Entity entityB) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		relationStorage.Remove(entityA, entityB);
-	}
-
-	public void UnrelateAll<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		relationStorage.RemoveEntity(entity);
-	}
-
-	public bool Related<T>(in Entity entityA, in Entity entityB) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.Has(entityA, entityB);
-	}
-
-	public T GetRelationData<T>(in Entity entityA, in Entity entityB) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.Get<T>(entityA, entityB);
-	}
-
-	public ReverseSpanEnumerator<(Entity, Entity)> Relations<T>() where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.All();
-	}
-
-	public ReverseSpanEnumerator<Entity> OutRelations<T>(Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.OutRelations(entity);
-	}
-
-	public Entity OutRelationSingleton<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.OutFirst(entity);
-	}
-
-	public bool HasOutRelation<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.HasOutRelation(entity);
-	}
-
-	public int OutRelationCount<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.OutRelationCount(entity);
-	}
-
-	public Entity NthOutRelation<T>(in Entity entity, int n) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.OutNth(entity, n);
-	}
-
-	public ReverseSpanEnumerator<Entity> InRelations<T>(Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.InRelations(entity);
-	}
-
-	public Entity InRelationSingleton<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.InFirst(entity);
-	}
-
-	public bool HasInRelation<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.HasInRelation(entity);
-	}
-
-	public int InRelationCount<T>(in Entity entity) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.InRelationCount(entity);
-	}
-
-	public Entity NthInRelation<T>(in Entity entity, int n) where T : unmanaged
-	{
-		var relationStorage = GetRelationStorage<T>();
-		return relationStorage.InNth(entity, n);
-	}
-
-	// MESSAGES
-
-	private MessageStorage GetMessageStorage<T>() where T : unmanaged
-	{
-		var typeId = new TypeId(MessageTypeIdAssigner<T>.Id);
-
-		if (typeId < MessageIndex.Count)
-		{
-			return MessageIndex[typeId];
-		}
-
-		for (var i = MessageIndex.Count; i <= typeId; i += 1)
-		{
-			MessageIndex.Add(new MessageStorage(MessageTypeElementSizes[i]));
-		}
-
-		return MessageIndex[typeId];
-	}
-
-	public void Send<T>(in T message) where T : unmanaged
-	{
-		GetMessageStorage<T>().Add(message);
-	}
-
-	public bool SomeMessage<T>() where T : unmanaged
-	{
-		return GetMessageStorage<T>().Some();
-	}
-
-	public ReadOnlySpan<T> ReadMessages<T>() where T : unmanaged
-	{
-		return GetMessageStorage<T>().All<T>();
-	}
-
-	public T ReadMessage<T>() where T : unmanaged
-	{
-		return GetMessageStorage<T>().First<T>();
-	}
-
-	public void ClearMessages<T>() where T : unmanaged
-	{
-		GetMessageStorage<T>().Clear();
-	}
-
-	// TODO: temporary component storage?
-	public void FinishUpdate()
-	{
-		foreach (var messageStorage in MessageIndex)
-		{
-			messageStorage.Clear();
-		}
-	}
-
-	// DEBUG
-	// NOTE: these methods are very inefficient
-	// they should only be used in debugging contexts!!
-#if DEBUG
-	public ComponentTypeEnumerator Debug_GetAllComponentTypes(Entity entity)
-	{
-		return new ComponentTypeEnumerator(this, EntityComponentIndex[(int) entity.ID]);
-	}
-
-	public IEnumerable<Entity> Debug_GetEntities(Type componentType)
-	{
-		var baseGetComponentStorageMethod = typeof(World).GetMethod(nameof(World.GetComponentStorage), BindingFlags.NonPublic | BindingFlags.Instance)!;
-		var genericGetComponentStorageMethod = baseGetComponentStorageMethod.MakeGenericMethod(componentType);
-		var storage = genericGetComponentStorageMethod.Invoke(this, null) as ComponentStorage;
-		return storage!.Debug_GetEntities();
-	}
-
-	public IEnumerable<Type> Debug_SearchComponentType(string typeString)
-	{
-		foreach (var type in ComponentTypeToId.Keys)
-		{
-			if (type.ToString().ToLower().Contains(typeString.ToLower()))
-			{
-				yield return type;
-			}
-		}
-	}
-
-	public ref struct ComponentTypeEnumerator
-	{
-		private World World;
-		private IndexableSet<TypeId> Types;
-		private int ComponentIndex;
-
-		public ComponentTypeEnumerator GetEnumerator() => this;
-
-		internal ComponentTypeEnumerator(
-			World world,
-			IndexableSet<TypeId> types
-		)
-		{
-			World = world;
-			Types = types;
-			ComponentIndex = -1;
-		}
-
-		public bool MoveNext()
-		{
-			ComponentIndex += 1;
-			return ComponentIndex < Types.Count;
-		}
-
-		public Type Current => ComponentTypeIdToType[Types[ComponentIndex]];
-	}
-#endif
-
-	protected virtual void Dispose(bool disposing)
-	{
-		if (!IsDisposed)
-		{
-			if (disposing)
-			{
-				foreach (var componentStorage in ComponentIndex)
-				{
-					componentStorage.Dispose();
-				}
-
-				foreach (var relationStorage in RelationIndex)
-				{
-					relationStorage.Dispose();
-				}
-
-				foreach (var messageStorage in MessageIndex)
-				{
-					messageStorage.Dispose();
-				}
-
-				foreach (var componentSet in EntityComponentIndex)
-				{
-					componentSet.Dispose();
-				}
-
-				foreach (var relationSet in EntityRelationIndex)
-				{
-					relationSet.Dispose();
-				}
-
-				foreach (var filter in FilterIndex.Values)
-				{
-					filter.Dispose();
-				}
-
-				EntityIdAssigner.Dispose();
+				ComponentDepot.Remove(entity.ID, componentTypeIndex);
+				FilterStorage.RemoveEntity(entity.ID, componentTypeIndex);
 			}
 
-			IsDisposed = true;
+			foreach (var relationTypeIndex in EntityStorage.RelationTypeIndices(entity.ID))
+			{
+				RelationDepot.UnrelateAll(entity.ID, relationTypeIndex);
+			}
+
+			EntityStorage.Destroy(entity);
 		}
-	}
 
-	// // TODO: override finalizer only if 'Dispose(bool disposing)' has code to free unmanaged resources
-	// ~World()
-	// {
-	//     // Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-	//     Dispose(disposing: false);
-	// }
 
-	public void Dispose()
-	{
-		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
-		Dispose(disposing: true);
-		GC.SuppressFinalize(this);
+		public void FinishUpdate()
+		{
+			MessageDepot.Clear();
+		}
+
+		public Snapshot CreateSnapshot()
+		{
+			return new Snapshot(this);
+		}
 	}
 }