reset entity tag on Destroy

Did some storage restructuring to avoid dictionary lookups. This should be a fairly significant speedup, particularly on the type lookups which now use a clever static generic lookup.

Reviewed-on: #7

LICENSE.txt

@@ -0,0 +1,23 @@
+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

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

src/Collections/IndexableSet.cs

@@ -0,0 +1,106 @@
+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

@@ -0,0 +1,120 @@
+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

@@ -0,0 +1,121 @@
+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

@@ -1,303 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-
-namespace MoonTools.ECS
-{
-	internal class ComponentDepot
-	{
-		private Dictionary<Type, ComponentStorage> storages = new Dictionary<Type, ComponentStorage>();
-
-		private Dictionary<FilterSignature, IndexableSet<int>> filterSignatureToEntityIDs = new Dictionary<FilterSignature, IndexableSet<int>>();
-
-		private Dictionary<Type, HashSet<FilterSignature>> typeToFilterSignatures = new Dictionary<Type, HashSet<FilterSignature>>();
-
-#if DEBUG
-		private Dictionary<Type, Filter> singleComponentFilters = new Dictionary<Type, Filter>();
-#endif
-
-		private HashSet<Type> TypesWithDisabledSerialization = new HashSet<Type>();
-
-		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		internal void Register<TComponent>() where TComponent : unmanaged
-		{
-			if (!storages.ContainsKey(typeof(TComponent)))
-			{
-				storages.Add(typeof(TComponent), new ComponentStorage<TComponent>());
-#if DEBUG
-				singleComponentFilters.Add(typeof(TComponent), CreateFilter(new HashSet<Type>() { typeof(TComponent) }, new HashSet<Type>()));
-#endif
-			}
-		}
-
-		private ComponentStorage Lookup(Type type)
-		{
-			return storages[type];
-		}
-
-		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		private ComponentStorage<TComponent> Lookup<TComponent>() where TComponent : unmanaged
-		{
-			// TODO: is it possible to optimize this?
-			Register<TComponent>();
-			return (ComponentStorage<TComponent>) storages[typeof(TComponent)];
-		}
-
-		public bool Some<TComponent>() where TComponent : unmanaged
-		{
-			return Lookup<TComponent>().Any();
-		}
-
-		public bool Has<TComponent>(int entityID) where TComponent : unmanaged
-		{
-			return Lookup<TComponent>().Has(entityID);
-		}
-
-		private bool Has(Type type, int entityID)
-		{
-			return Lookup(type).Has(entityID);
-		}
-
-		public ref readonly TComponent Get<TComponent>(int entityID) where TComponent : unmanaged
-		{
-			return ref Lookup<TComponent>().Get(entityID);
-		}
-
-		public ref readonly TComponent Get<TComponent>() where TComponent : unmanaged
-		{
-			return ref Lookup<TComponent>().Get();
-		}
-
-		public void Set<TComponent>(int entityID, in TComponent component) where TComponent : unmanaged
-		{
-			var existed = Lookup<TComponent>().Set(entityID, component);
-
-			// update filters
-			if (!existed)
-			{
-				if (typeToFilterSignatures.TryGetValue(typeof(TComponent), out var filterSignatures))
-				{
-					foreach (var filterSignature in filterSignatures)
-					{
-						CheckFilter(filterSignature, entityID);
-					}
-				}
-			}
-		}
-
-		public Entity GetSingletonEntity<TComponent>() where TComponent : unmanaged
-		{
-			return Lookup<TComponent>().FirstEntity();
-		}
-
-		public ReadOnlySpan<TComponent> ReadComponents<TComponent>() where TComponent : unmanaged
-		{
-			return Lookup<TComponent>().AllComponents();
-		}
-
-		private void Remove(Type type, int entityID)
-		{
-			var existed = Lookup(type).Remove(entityID);
-
-			// update filters
-			if (existed)
-			{
-				if (typeToFilterSignatures.TryGetValue(type, out var filterSignatures))
-				{
-					foreach (var filterSignature in filterSignatures)
-					{
-						CheckFilter(filterSignature, entityID);
-					}
-				}
-			}
-		}
-
-		public void Remove<TComponent>(int entityID) where TComponent : unmanaged
-		{
-			var existed = Lookup<TComponent>().Remove(entityID);
-
-			// update filters
-			if (existed)
-			{
-				if (typeToFilterSignatures.TryGetValue(typeof(TComponent), out var filterSignatures))
-				{
-					foreach (var filterSignature in filterSignatures)
-					{
-						CheckFilter(filterSignature, entityID);
-					}
-				}
-			}
-		}
-
-		// TODO: is there some way to optimize this without complicating serialization?
-		public void OnEntityDestroy(int entityID)
-		{
-			foreach (var type in storages.Keys)
-			{
-				Remove(type, entityID);
-			}
-		}
-
-		public Filter CreateFilter(HashSet<Type> included, HashSet<Type> excluded)
-		{
-			var filterSignature = new FilterSignature(included, excluded);
-			if (!filterSignatureToEntityIDs.ContainsKey(filterSignature))
-			{
-				filterSignatureToEntityIDs.Add(filterSignature, new IndexableSet<int>());
-
-				foreach (var type in included)
-				{
-					if (!typeToFilterSignatures.ContainsKey(type))
-					{
-						typeToFilterSignatures.Add(type, new HashSet<FilterSignature>());
-					}
-
-					typeToFilterSignatures[type].Add(filterSignature);
-				}
-
-				foreach (var type in excluded)
-				{
-					if (!typeToFilterSignatures.ContainsKey(type))
-					{
-						typeToFilterSignatures.Add(type, new HashSet<FilterSignature>());
-					}
-
-					typeToFilterSignatures[type].Add(filterSignature);
-				}
-			}
-			return new Filter(this, included, excluded);
-		}
-
-		// FIXME: this dictionary should probably just store entities
-		public IEnumerable<Entity> FilterEntities(Filter filter)
-		{
-			foreach (var id in filterSignatureToEntityIDs[filter.Signature])
-			{
-				yield return new Entity(id);
-			}
-		}
-
-		public IEnumerable<Entity> FilterEntitiesRandom(Filter filter)
-		{
-			foreach (var index in RandomGenerator.LinearCongruentialGenerator(FilterCount(filter)))
-			{
-				yield return new Entity(filterSignatureToEntityIDs[filter.Signature][index]);
-			}
-		}
-
-		public Entity FilterNthEntity(Filter filter, int index)
-		{
-			return new Entity(filterSignatureToEntityIDs[filter.Signature][index]);
-		}
-
-		public Entity FilterRandomEntity(Filter filter)
-		{
-			var randomIndex = RandomGenerator.Next(FilterCount(filter));
-			return new Entity(filterSignatureToEntityIDs[filter.Signature][randomIndex]);
-		}
-
-		public int FilterCount(Filter filter)
-		{
-			return filterSignatureToEntityIDs[filter.Signature].Count;
-		}
-
-		private void CheckFilter(FilterSignature filterSignature, int entityID)
-		{
-			foreach (var type in filterSignature.Included)
-			{
-				if (!Has(type, entityID))
-				{
-					filterSignatureToEntityIDs[filterSignature].Remove(entityID);
-					return;
-				}
-			}
-
-			foreach (var type in filterSignature.Excluded)
-			{
-				if (Has(type, entityID))
-				{
-					filterSignatureToEntityIDs[filterSignature].Remove(entityID);
-					return;
-				}
-			}
-
-			filterSignatureToEntityIDs[filterSignature].Add(entityID);
-		}
-
-		public void DisableSerialization<TComponent>() where TComponent : unmanaged
-		{
-			TypesWithDisabledSerialization.Add(typeof(TComponent));
-		}
-
-		public void Save(ComponentDepotState state)
-		{
-			foreach (var (type, storage) in storages)
-			{
-				if (!TypesWithDisabledSerialization.Contains(type))
-				{
-					if (!state.StorageStates.ContainsKey(type))
-					{
-						state.StorageStates.Add(type, storage.CreateState());
-					}
-
-					storage.Save(state.StorageStates[type]);
-				}
-			}
-
-			foreach (var (signature, set) in filterSignatureToEntityIDs)
-			{
-				// FIXME: we could cache this
-				if (!signature.Included.Overlaps(TypesWithDisabledSerialization) && !signature.Excluded.Overlaps(TypesWithDisabledSerialization))
-				{
-					if (!state.FilterStates.ContainsKey(signature))
-					{
-						state.FilterStates[signature] = new IndexableSetState<int>(set.Count);
-					}
-					set.Save(state.FilterStates[signature]);
-				}
-			}
-		}
-
-		public void Load(ComponentDepotState state)
-		{
-			foreach (var (type, storageState) in state.StorageStates)
-			{
-				storages[type].Load(storageState);
-			}
-
-			foreach (var (signature, setState) in state.FilterStates)
-			{
-				filterSignatureToEntityIDs[signature].Load(setState);
-			}
-		}
-
-#if DEBUG
-		public IEnumerable<object> Debug_GetAllComponents(int entityID)
-		{
-			foreach (var (type, storage) in storages)
-			{
-				if (storage.Has(entityID))
-				{
-					yield return storage.Debug_Get(entityID);
-				}
-			}
-		}
-
-		public IEnumerable<Entity> Debug_GetEntities(Type componentType)
-		{
-			return singleComponentFilters[componentType].Entities;
-		}
-
-		public IEnumerable<Type> Debug_SearchComponentType(string typeString)
-		{
-			foreach (var type in storages.Keys)
-			{
-				if (type.ToString().ToLower().Contains(typeString.ToLower()))
-				{
-					yield return type;
-				}
-			}
-		}
-#endif
-	}
-}

src/ComponentStorage.cs

@@ -1,170 +1,142 @@
 using System;
 using System.Collections.Generic;
-using System.Runtime.InteropServices;
+using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS
+namespace MoonTools.ECS;
+
+internal class ComponentStorage : IDisposable
 {
-	internal abstract class ComponentStorage
+	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)
 	{
-		public abstract bool Has(int entityID);
-		public abstract bool Remove(int entityID);
-		public abstract object Debug_Get(int entityID);
-		public abstract ComponentStorageState CreateState();
-		public abstract void Save(ComponentStorageState state);
-		public abstract void Load(ComponentStorageState state);
+		ElementSize = elementSize;
+		Components = new NativeArray(elementSize);
+		EntityIDs = new NativeArray<Entity>();
+		TypeId = typeId;
 	}
 
-	internal class ComponentStorage<TComponent> : ComponentStorage where TComponent : unmanaged
+	public bool Any()
 	{
-		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];
+		return Components.Count > 0;
+	}
 
-		public bool Any()
-		{
-			return nextID > 0;
-		}
+	public bool Has(Entity entity)
+	{
+		return EntityIDToStorageIndex.ContainsKey(entity);
+	}
 
-		public override bool Has(int entityID)
-		{
-			return entityIDToStorageIndex.ContainsKey(entityID);
-		}
+	public ref T Get<T>(in Entity entity) where T : unmanaged
+	{
+		return ref Components.Get<T>(EntityIDToStorageIndex[entity]);
+	}
 
-		public ref readonly TComponent Get(int entityID)
-		{
-			return ref components[entityIDToStorageIndex[entityID]];
-		}
-
-		public override object Debug_Get(int entityID)
-		{
-			return components[entityIDToStorageIndex[entityID]];
-		}
-
-		public ref readonly TComponent Get()
-		{
+	public ref T GetFirst<T>() where T : unmanaged
+	{
 #if DEBUG
-			if (nextID == 0)
-			{
-				throw new IndexOutOfRangeException("Component storage is empty!");
-			}
+		if (Components.Count == 0)
+		{
+			throw new IndexOutOfRangeException("Component storage is empty!");
+		}
 #endif
-			return ref components[0];
-		}
+		return ref Components.Get<T>(0);
+	}
 
-		// Returns true if the entity already had this component.
-		public bool Set(int entityID, in TComponent component)
+	// Returns true if the entity had this component.
+	public bool Set<T>(in Entity entity, in T component) where T : unmanaged
+	{
+		if (EntityIDToStorageIndex.TryGetValue(entity, out var index))
 		{
-			bool result = true;
-
-			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;
-
-				result = false;
-			}
-
-			components[entityIDToStorageIndex[entityID]] = component;
-
-			return result;
+			Components.Set(index, component);
+			return true;
 		}
-
-		// Returns true if the entity had this component.
-		public override bool Remove(int entityID)
+		else
 		{
-			if (entityIDToStorageIndex.ContainsKey(entityID))
-			{
-				var storageIndex = entityIDToStorageIndex[entityID];
-				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;
-			}
-
+			EntityIDToStorageIndex[entity] = Components.Count;
+			EntityIDs.Append(entity);
+			Components.Append(component);
 			return false;
 		}
+	}
 
-		public void Clear()
+	// Returns true if the entity had this component.
+	public bool Remove(in Entity entity)
+	{
+		if (EntityIDToStorageIndex.TryGetValue(entity, out int index))
 		{
-			nextID = 0;
-			entityIDToStorageIndex.Clear();
+			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)
+			{
+				EntityIDToStorageIndex[lastEntity] = index;
+			}
+
+			return true;
 		}
 
-		public ReadOnlySpan<TComponent> AllComponents()
-		{
-			return new ReadOnlySpan<TComponent>(components, 0, nextID);
-		}
+		return false;
+	}
 
-		public Entity FirstEntity()
-		{
+	public void Clear()
+	{
+		Components.Clear();
+		EntityIDs.Clear();
+		EntityIDToStorageIndex.Clear();
+	}
+
+	public Entity FirstEntity()
+	{
 #if DEBUG
-			if (nextID == 0)
-			{
-				throw new IndexOutOfRangeException("Component storage is empty!");
-			}
+		if (EntityIDs.Count == 0)
+		{
+			throw new IndexOutOfRangeException("Component storage is empty!");
+		}
 #endif
-			return new Entity(entityIDs[0]);
-		}
+		return EntityIDs[0];
+	}
 
-		public override ComponentStorageState CreateState()
+#if DEBUG
+	internal IEnumerable<Entity> Debug_GetEntities()
+	{
+		return EntityIDToStorageIndex.Keys;
+	}
+#endif
+
+	protected virtual void Dispose(bool disposing)
+	{
+		if (!IsDisposed)
 		{
-			return ComponentStorageState.Create<TComponent>(nextID);
-		}
+			Components.Dispose();
+			EntityIDs.Dispose();
 
-		public override void Save(ComponentStorageState state)
-		{
-			ReadOnlySpan<byte> entityIDBytes = MemoryMarshal.Cast<int, byte>(new ReadOnlySpan<int>(entityIDs, 0, nextID));
-
-			if (entityIDBytes.Length > state.EntityIDs.Length)
-			{
-				Array.Resize(ref state.EntityIDs, entityIDBytes.Length);
-			}
-			entityIDBytes.CopyTo(state.EntityIDs);
-
-			ReadOnlySpan<byte> componentBytes = MemoryMarshal.Cast<TComponent, byte>(AllComponents());
-			if (componentBytes.Length > state.Components.Length)
-			{
-				Array.Resize(ref state.Components, componentBytes.Length);
-			}
-			componentBytes.CopyTo(state.Components);
-
-			state.Count = nextID;
-		}
-
-		public override void Load(ComponentStorageState state)
-		{
-			state.EntityIDs.CopyTo(MemoryMarshal.Cast<int, byte>(entityIDs));
-			state.Components.CopyTo(MemoryMarshal.Cast<TComponent, byte>(components));
-
-			entityIDToStorageIndex.Clear();
-			for (var i = 0; i < state.Count; i += 1)
-			{
-				entityIDToStorageIndex[entityIDs[i]] = i;
-			}
-
-			nextID = state.Count;
+			IsDisposed = true;
 		}
 	}
+
+	// ~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);
+	}
 }

src/DebugSystem.cs

@@ -1,32 +1,17 @@
 // 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
+namespace MoonTools.ECS;
+
+public abstract class DebugSystem : System
 {
-	public abstract class DebugSystem : System
-	{
-		protected DebugSystem(World world) : base(world)
-		{
-		}
+	protected DebugSystem(World world) : base(world) { }
 
-		protected IEnumerable<object> Debug_GetAllComponents(Entity entity)
-		{
-			return ComponentDepot.Debug_GetAllComponents(entity.ID);
-		}
-
-		protected IEnumerable<Entity> Debug_GetEntities(Type componentType)
-		{
-			return ComponentDepot.Debug_GetEntities(componentType);
-		}
-
-		protected IEnumerable<Type> Debug_SearchComponentType(string typeString)
-		{
-			return ComponentDepot.Debug_SearchComponentType(typeString);
-		}
-	}
+	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);
 }
 #endif

src/Entity.cs

@@ -1,39 +1,3 @@
-using System;
+namespace MoonTools.ECS;
 
-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 readonly record struct Entity(uint ID);

src/EntityComponentReader.cs

@@ -1,106 +1,36 @@
-using System;
-using System.Collections.Generic;
+namespace MoonTools.ECS;
 
-namespace MoonTools.ECS
+public abstract class EntityComponentReader
 {
-	public abstract class EntityComponentReader
+	protected readonly World World;
+	public FilterBuilder FilterBuilder => World.FilterBuilder;
+
+	protected 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(ComponentDepot);
-
-		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
-		{
-			return ComponentDepot.Has<TComponent>(entity.ID);
-		}
-
-		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.Get<TComponent>();
-		}
-
-		protected Entity GetSingletonEntity<TComponent>() where TComponent : unmanaged
-		{
-			return ComponentDepot.GetSingletonEntity<TComponent>();
-		}
-
-		protected bool Exists(in Entity entity)
-		{
-			return EntityStorage.Exists(entity);
-		}
-
-		protected IEnumerable<(Entity, Entity, TRelationKind)> 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);
-		}
-
-		// relations go A->B, so given A, will give all outgoing B relations.
-		protected IEnumerable<(Entity, TRelationKind)> OutRelations<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
-		{
-			return RelationDepot.OutRelations<TRelationKind>(entity.ID);
-		}
-
-		protected (Entity, TRelationKind) 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 incoming A relations.
-		protected IEnumerable<(Entity, TRelationKind)> InRelations<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
-		{
-			return RelationDepot.InRelations<TRelationKind>(entity.ID);
-		}
-
-		protected (Entity, TRelationKind) 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);
-		}
+		World = world;
 	}
+
+	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

@@ -1,75 +0,0 @@
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-	internal class EntityStorage
-	{
-		private int nextID = 0;
-		private readonly Stack<int> availableIDs = new Stack<int>();
-		private readonly HashSet<int> availableIDHash = new HashSet<int>();
-
-		public Entity Create()
-		{
-			return new Entity(NextID());
-		}
-
-		public bool Exists(in Entity entity)
-		{
-			return Taken(entity.ID);
-		}
-
-		public void Destroy(in Entity entity)
-		{
-			Release(entity.ID);
-		}
-
-		public void Save(EntityStorageState state)
-		{
-			state.NextID = nextID;
-			state.availableIDs.Clear();
-			foreach (var id in availableIDs)
-			{
-				state.availableIDs.Add(id);
-			}
-		}
-
-		public void Load(EntityStorageState state)
-		{
-			nextID = state.NextID;
-			availableIDs.Clear();
-			availableIDHash.Clear();
-			foreach (var id in state.availableIDs)
-			{
-				availableIDs.Push(id);
-				availableIDHash.Add(id);
-			}
-		}
-
-		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

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

src/Filter.cs

@@ -1,27 +1,123 @@
 using System;
-using System.Collections.Generic;
+using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS
+namespace MoonTools.ECS;
+
+public class Filter
 {
-	public class Filter
-	{
-		internal FilterSignature Signature;
-		private ComponentDepot ComponentDepot;
+	private World World;
+	internal FilterSignature Signature;
 
-		internal Filter(ComponentDepot componentDepot, HashSet<Type> included, HashSet<Type> excluded)
+	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)
+	{
+		World = world;
+		Signature = signature;
+	}
+
+	public void DestroyAllEntities()
+	{
+		foreach (var entity in EntitySet)
 		{
-			ComponentDepot = componentDepot;
-			Signature = new FilterSignature(included, excluded);
+			World.Destroy(entity);
+		}
+	}
+
+	internal void Check(Entity entity)
+	{
+		foreach (var type in Signature.Included)
+		{
+			if (!World.Has(entity, type))
+			{
+				EntitySet.Remove(entity);
+				return;
+			}
 		}
 
-		public IEnumerable<Entity> Entities => ComponentDepot.FilterEntities(this);
-		public IEnumerable<Entity> EntitiesInRandomOrder => ComponentDepot.FilterEntitiesRandom(this);
-		public Entity RandomEntity => ComponentDepot.FilterRandomEntity(this);
+		foreach (var type in Signature.Excluded)
+		{
+			if (World.Has(entity, type))
+			{
+				EntitySet.Remove(entity);
+				return;
+			}
+		}
 
-		public int Count => ComponentDepot.FilterCount(this);
-		public bool Empty => Count == 0;
+		EntitySet.Add(entity);
+	}
 
-		// WARNING: this WILL crash if the index is out of range!
-		public Entity NthEntity(int index) => ComponentDepot.FilterNthEntity(this, index);
+	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);
 	}
 }

src/FilterBuilder.cs

@@ -1,45 +1,43 @@
-using System;
-using System.Collections.Generic;
+using MoonTools.ECS.Collections;
 
 namespace MoonTools.ECS
 {
 	public struct FilterBuilder
 	{
-		private ComponentDepot ComponentDepot;
-		private HashSet<Type> Included;
-		private HashSet<Type> Excluded;
+		World World;
+		IndexableSet<TypeId> Included;
+		IndexableSet<TypeId> Excluded;
 
-		internal FilterBuilder(ComponentDepot componentDepot)
+		internal FilterBuilder(World world)
 		{
-			ComponentDepot = componentDepot;
-			Included = new HashSet<Type>();
-			Excluded = new HashSet<Type>();
+			World = world;
+			Included = new IndexableSet<TypeId>();
+			Excluded = new IndexableSet<TypeId>();
 		}
 
-		private FilterBuilder(ComponentDepot componentDepot, HashSet<Type> included, HashSet<Type> excluded)
+		private FilterBuilder(World world, IndexableSet<TypeId> included, IndexableSet<TypeId> excluded)
 		{
-			ComponentDepot = componentDepot;
+			World = world;
 			Included = included;
 			Excluded = excluded;
 		}
 
-		public FilterBuilder Include<TComponent>() where TComponent : unmanaged
+		public FilterBuilder Include<T>() where T : unmanaged
 		{
-			ComponentDepot.Register<TComponent>();
-			Included.Add(typeof(TComponent));
-			return new FilterBuilder(ComponentDepot, Included, Excluded);
+			Included.Add(World.GetComponentTypeId<T>());
+			return new FilterBuilder(World, Included, Excluded);
 		}
 
-		public FilterBuilder Exclude<TComponent>() where TComponent : unmanaged
+		public FilterBuilder Exclude<T>() where T : unmanaged
 		{
-			ComponentDepot.Register<TComponent>();
-			Excluded.Add(typeof(TComponent));
-			return new FilterBuilder(ComponentDepot, Included, Excluded);
+			Excluded.Add(World.GetComponentTypeId<T>());
+			return new FilterBuilder(World, Included, Excluded);
 		}
 
 		public Filter Build()
 		{
-			return ComponentDepot.CreateFilter(Included, Excluded);
+			var signature = new FilterSignature(Included, Excluded);
+			return World.GetFilter(signature);
 		}
 	}
 }

src/FilterSignature.cs

@@ -1,51 +1,69 @@
 using System;
-using System.Collections.Generic;
+using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS
+namespace MoonTools.ECS;
+
+public struct FilterSignature : IEquatable<FilterSignature>
 {
-	public struct FilterSignature
+	public readonly IndexableSet<TypeId> Included;
+	public readonly IndexableSet<TypeId> Excluded;
+
+	public FilterSignature(IndexableSet<TypeId> included, IndexableSet<TypeId> excluded)
 	{
-		private const int HASH_FACTOR = 97;
+		Included = included;
+		Excluded = excluded;
+	}
 
-		public readonly HashSet<Type> Included;
-		public readonly HashSet<Type> Excluded;
+	public override bool Equals(object? obj)
+	{
+		return obj is FilterSignature signature && Equals(signature);
+	}
 
-		public FilterSignature(HashSet<Type> included, HashSet<Type> excluded)
+	public bool Equals(FilterSignature other)
+	{
+		foreach (var included in Included)
 		{
-			Included = included;
-			Excluded = excluded;
-		}
-
-		public override bool Equals(object? obj)
-		{
-			return obj is FilterSignature signature && Equals(signature);
-		}
-
-		public bool Equals(FilterSignature other)
-		{
-			return Included.SetEquals(other.Included) && Excluded.SetEquals(other.Excluded);
-		}
-
-		private int GuidToInt(Guid guid)
-		{
-			return BitConverter.ToInt32(guid.ToByteArray());
-		}
-
-		public override int GetHashCode()
-		{
-			int result = 1;
-			foreach (var type in Included)
+			if (!other.Included.Contains(included))
 			{
-				result *= HASH_FACTOR + GuidToInt(type.GUID);
+				return false;
 			}
-
-			// FIXME: Is there a way to avoid collisions when this is the same set as included?
-			foreach (var type in Excluded)
-			{
-				result *= HASH_FACTOR + GuidToInt(type.GUID);
-			}
-
-			return result;
 		}
+
+		foreach (var excluded in Excluded)
+		{
+			if (!other.Excluded.Contains(excluded))
+			{
+				return false;
+			}
+		}
+
+		return true;
+	}
+
+	public override int GetHashCode()
+	{
+		var hashcode = 1;
+
+		foreach (var type in Included)
+		{
+			hashcode = HashCode.Combine(hashcode, type);
+		}
+
+		foreach (var type in Excluded)
+		{
+			hashcode = HashCode.Combine(hashcode, type);
+		}
+
+		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/IHasEntity.cs

@@ -1,7 +0,0 @@
-namespace MoonTools.ECS
-{
-	public interface IHasEntity
-	{
-		Entity Entity { get; }
-	}
-}

src/IdAssigner.cs

@@ -0,0 +1,62 @@
+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

@@ -1,115 +0,0 @@
-using System;
-using System.Collections;
-using System.Collections.Generic;
-using System.Runtime.InteropServices;
-
-namespace MoonTools.ECS
-{
-	internal class IndexableSet<T> : IEnumerable<T> where T : unmanaged
-	{
-		private Dictionary<T, int> indices;
-		private T[] array;
-		public int Count { get; private set; }
-
-		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 IEnumerator<T> GetEnumerator()
-		{
-			for (var i = Count - 1; i >= 0; i -= 1)
-			{
-				yield return array[i];
-			}
-		}
-
-		IEnumerator IEnumerable.GetEnumerator()
-		{
-			for (var i = Count - 1; i >= 0; i -= 1)
-			{
-				yield return array[i];
-			}
-		}
-
-		public void Clear()
-		{
-			Count = 0;
-		}
-
-		public void Save(IndexableSetState<T> state)
-		{
-			ReadOnlySpan<byte> arrayBytes = MemoryMarshal.Cast<T, byte>(array);
-
-			if (arrayBytes.Length > state.Array.Length)
-			{
-				Array.Resize(ref state.Array, arrayBytes.Length);
-			}
-
-			arrayBytes.CopyTo(state.Array);
-
-			state.Count = Count;
-		}
-
-		public void Load(IndexableSetState<T> state)
-		{
-			state.Array.CopyTo(MemoryMarshal.Cast<T, byte>(array));
-
-			indices.Clear();
-			for (var i = 0; i < state.Count; i += 1)
-			{
-				indices[array[i]] = i;
-			}
-
-			Count = state.Count;
-		}
-	}
-}

src/Manipulator.cs

@@ -0,0 +1,20 @@
+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

@@ -1,63 +0,0 @@
-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 : struct
-		{
-			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 : struct
-		{
-			Lookup<TMessage>().Add(message);
-		}
-
-		public bool Some<TMessage>() where TMessage : struct
-		{
-			return Lookup<TMessage>().Some();
-		}
-
-		public ReadOnlySpan<TMessage> All<TMessage>() where TMessage : struct
-		{
-			return Lookup<TMessage>().All();
-		}
-
-		public TMessage First<TMessage>() where TMessage : struct
-		{
-			return Lookup<TMessage>().First();
-		}
-
-		public IEnumerable<TMessage> WithEntity<TMessage>(int entityID) where TMessage : struct, IHasEntity
-		{
-			return Lookup<TMessage>().WithEntity(entityID);
-		}
-
-		public ref readonly TMessage FirstWithEntity<TMessage>(int entityID) where TMessage : struct, IHasEntity
-		{
-			return ref Lookup<TMessage>().FirstWithEntity(entityID);
-		}
-
-		public bool SomeWithEntity<TMessage>(int entityID) where TMessage : struct, IHasEntity
-		{
-			return Lookup<TMessage>().SomeWithEntity(entityID);
-		}
-
-		public void Clear()
-		{
-			foreach (var storage in storages.Values)
-			{
-				storage.Clear();
-			}
-		}
-	}
-}

src/MessageStorage.cs

@@ -1,91 +1,63 @@
 using System;
-using System.Collections.Generic;
+using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS
+namespace MoonTools.ECS;
+
+public class MessageStorage : IDisposable
 {
-	internal abstract class MessageStorage
+	private NativeArray Messages;
+
+	private bool IsDisposed;
+
+	public MessageStorage(int elementSize)
 	{
-		public abstract void Clear();
+		Messages = new NativeArray(elementSize);
 	}
 
-	internal class MessageStorage<TMessage> : MessageStorage where TMessage : struct
+	public void Add<T>(in T message) where T : unmanaged
 	{
-		private int count = 0;
-		private int capacity = 128;
-		private TMessage[] messages;
-		private Dictionary<int, List<int>> entityToIndices = new Dictionary<int, List<int>>();
+		Messages.Append(message);
+	}
 
-		public MessageStorage()
+	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)
 		{
-			messages = new TMessage[capacity];
+			Messages.Dispose();
+			IsDisposed = true;
 		}
+	}
 
-		public void Add(in TMessage message)
-		{
-			if (count == capacity)
-			{
-				capacity *= 2;
-				Array.Resize(ref messages, capacity);
-			}
+	// ~MessageStorage()
+	// {
+	// 	// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
+	// 	Dispose(disposing: false);
+	// }
 
-			messages[count] = message;
-
-			if (message is IHasEntity entityMessage)
-			{
-				if (!entityToIndices.ContainsKey(entityMessage.Entity.ID))
-				{
-					entityToIndices.Add(entityMessage.Entity.ID, new List<int>());
-				}
-
-				entityToIndices[entityMessage.Entity.ID].Add(count);
-			}
-
-			count += 1;
-		}
-
-		public bool Some()
-		{
-			return count > 0;
-		}
-
-		public ReadOnlySpan<TMessage> All()
-		{
-			return new ReadOnlySpan<TMessage>(messages, 0, count);
-		}
-
-		public TMessage First()
-		{
-			return messages[0];
-		}
-
-		public IEnumerable<TMessage> WithEntity(int entityID)
-		{
-			if (entityToIndices.ContainsKey(entityID))
-			{
-				foreach (var index in entityToIndices[entityID])
-				{
-					yield return messages[index];
-				}
-			}
-		}
-
-		public ref readonly TMessage FirstWithEntity(int entityID)
-		{
-			return ref messages[entityToIndices[entityID][0]];
-		}
-
-		public bool SomeWithEntity(int entityID)
-		{
-			return entityToIndices.ContainsKey(entityID) && entityToIndices[entityID].Count > 0;
-		}
-
-		public override void Clear()
-		{
-			count = 0;
-			foreach (var set in entityToIndices.Values)
-			{
-				set.Clear();
-			}
-		}
+	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

@@ -1,40 +1,208 @@
-using System;
-using System.Collections.Generic;
+using System;
+using System.Runtime.CompilerServices;
 
-namespace MoonTools.ECS
+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
 {
-	internal static class RandomGenerator
+	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()
 	{
-		private static Random random = new Random();
+		Init((uint) Environment.TickCount);
+	}
 
-		private static int[] Primes =
+	/// <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++)
 		{
-			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);
+			s = (((s * 214013 + 2531011) >> 16) & 0x7fffffff) | 0;
+			State[i] = ~ ~s; //i ;
 		}
+		Index = 0;
+	}
 
-		/// <summary>
-		/// A psuedorandom nonrepeating sequence of integers from 0 to n.
-		/// </summary>
-		public static IEnumerable<int> LinearCongruentialGenerator(int n)
+	/// <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)
 		{
-			var x = Primes[random.Next(Primes.Length - 1)];
-			while (x % n == 0)
+			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)
 			{
-				// not coprime, try again
-				x = Primes[random.Next(Primes.Length - 1)];
+				Unsafe.Write(ptr + offset, State[i]);
+				offset += 4;
 			}
 
-			var start = random.Next(n);
-
-			for (var i = start; i < start + n; i++)
-			{
-				yield return (i * x) % n;
-			}
+			Unsafe.Write(ptr + offset, Index);
 		}
 	}
+
+	/// <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)
+	{
+#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)
+			{
+				State[i] = Unsafe.Read<uint>(ptr + offset);
+				offset += 4;
+			}
+
+			Index = Unsafe.Read<uint>(ptr + offset);
+		}
+	}
+
+	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;
+	}
 }

src/RandomManager.cs

@@ -0,0 +1,81 @@
+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/Relation.cs

@@ -1,37 +0,0 @@
-using System;
-
-namespace MoonTools.ECS
-{
-	internal struct Relation : IEquatable<Relation>
-	{
-		public Entity A { get; }
-		public Entity B { get; }
-
-		internal Relation(Entity entityA, Entity entityB)
-		{
-			A = entityA;
-			B = entityB;
-		}
-
-		internal Relation(int idA, int idB)
-		{
-			A = new Entity(idA);
-			B = new Entity(idB);
-		}
-
-		public override bool Equals(object? obj)
-		{
-			return obj is Relation relation && Equals(relation);
-		}
-
-		public bool Equals(Relation other)
-		{
-			return A.ID == other.A.ID && B.ID == other.B.ID;
-		}
-
-		public override int GetHashCode()
-		{
-			return HashCode.Combine(A.ID, B.ID);
-		}
-	}
-}

src/RelationDepot.cs

@@ -1,121 +0,0 @@
-using System;
-using System.Collections.Generic;
-using System.Runtime.CompilerServices;
-
-namespace MoonTools.ECS
-{
-	internal class RelationDepot
-	{
-		private Dictionary<Type, RelationStorage> storages = new Dictionary<Type, RelationStorage>();
-
-		private void Register<TRelationKind>() where TRelationKind : unmanaged
-		{
-			if (!storages.ContainsKey(typeof(TRelationKind)))
-			{
-				storages.Add(typeof(TRelationKind), new RelationStorage<TRelationKind>());
-			}
-		}
-
-		[MethodImpl(MethodImplOptions.AggressiveInlining)]
-		private RelationStorage<TRelationKind> Lookup<TRelationKind>() where TRelationKind : unmanaged
-		{
-			Register<TRelationKind>();
-			return (RelationStorage<TRelationKind>) storages[typeof(TRelationKind)];
-		}
-
-		public void Set<TRelationKind>(Relation relation, TRelationKind relationData) where TRelationKind : unmanaged
-		{
-			Lookup<TRelationKind>().Set(relation, relationData);
-		}
-
-		public void Remove<TRelationKind>(Relation relation) where TRelationKind : unmanaged
-		{
-			Lookup<TRelationKind>().Remove(relation);
-		}
-
-		public void UnrelateAll<TRelationKind>(int entityID) where TRelationKind : unmanaged
-		{
-			Lookup<TRelationKind>().UnrelateAll(entityID);
-		}
-
-		// FIXME: optimize this
-		public void OnEntityDestroy(int entityID)
-		{
-			foreach (var storage in storages.Values)
-			{
-				storage.OnEntityDestroy(entityID);
-			}
-		}
-
-		public IEnumerable<(Entity, Entity, TRelationKind)> Relations<TRelationKind>() where TRelationKind : unmanaged
-		{
-			return Lookup<TRelationKind>().All();
-		}
-
-		public bool Related<TRelationKind>(int idA, int idB) where TRelationKind : unmanaged
-		{
-			return Lookup<TRelationKind>().Has(new Relation(idA, idB));
-		}
-
-		public IEnumerable<(Entity, TRelationKind)> OutRelations<TRelationKind>(int entityID) where TRelationKind : unmanaged
-		{
-			return Lookup<TRelationKind>().OutRelations(entityID);
-		}
-
-		public (Entity, TRelationKind) 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 IEnumerable<(Entity, TRelationKind)> InRelations<TRelationKind>(int entityID) where TRelationKind : unmanaged
-		{
-			return Lookup<TRelationKind>().InRelations(entityID);
-		}
-
-		public (Entity, TRelationKind) 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 int InRelationCount<TRelationKind>(int entityID) where TRelationKind : unmanaged
-		{
-			return Lookup<TRelationKind>().InRelationCount(entityID);
-		}
-
-		public void Save(RelationDepotState state)
-		{
-			foreach (var (type, storage) in storages)
-			{
-				if (!state.StorageStates.ContainsKey(type))
-				{
-					state.StorageStates.Add(type, storage.CreateState());
-				}
-
-				storage.Save(state.StorageStates[type]);
-			}
-		}
-
-		public void Load(RelationDepotState state)
-		{
-			foreach (var (type, storageState) in state.StorageStates)
-			{
-				storages[type].Load(storageState);
-			}
-		}
-	}
-}

src/RelationStorage.cs

@@ -1,282 +1,286 @@
 using System;
 using System.Collections.Generic;
-using System.Runtime.InteropServices;
+using System.Runtime.CompilerServices;
+using MoonTools.ECS.Collections;
 
-namespace MoonTools.ECS
+namespace MoonTools.ECS;
+
+// TODO: implement this entire class with NativeMemory equivalents, can just memcpy for snapshots
+internal class RelationStorage
 {
-	internal abstract class RelationStorage
+	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)
 	{
-		public abstract RelationStorageState CreateState();
-		public abstract void Save(RelationStorageState state);
-		public abstract void Load(RelationStorageState state);
-		public abstract void OnEntityDestroy(int entityID);
+		ElementSize = relationDataSize;
+		Relations = new NativeArray(Unsafe.SizeOf<(Entity, Entity)>());
+		RelationDatas = new NativeArray(relationDataSize);
 	}
 
-	// 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
+	public ReverseSpanEnumerator<(Entity, Entity)> All()
 	{
-		private int count = 0;
-		private Dictionary<Relation, int> indices = new Dictionary<Relation, int>(16);
-		private Relation[] relations = new Relation[16];
-		private TRelation[] relationDatas = new TRelation[16];
-		private Dictionary<int, IndexableSet<int>> outRelations = new Dictionary<int, IndexableSet<int>>(16);
-		private Dictionary<int, IndexableSet<int>> inRelations = new Dictionary<int, IndexableSet<int>>(16);
-		private Stack<IndexableSet<int>> listPool = new Stack<IndexableSet<int>>();
+		return new ReverseSpanEnumerator<(Entity, Entity)>(Relations.ToSpan<(Entity, Entity)>());
+	}
 
-		public IEnumerable<(Entity, Entity, TRelation)> All()
+	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))
 		{
-			for (var i = 0; i < count; i += 1)
-			{
-				var relation = relations[i];
-				yield return (relation.A, relation.B, relationDatas[i]);
-			}
+			RelationDatas.Set(index, relationData);
+			return;
 		}
 
-		public void Set(Relation relation, TRelation relationData)
+		if (!OutRelationSets.ContainsKey(entityA))
 		{
-			if (indices.ContainsKey(relation))
-			{
-				var index = indices[relation];
-				relationDatas[index] = relationData;
-				return;
-			}
-
-			var idA = relation.A.ID;
-			var idB = relation.B.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;
+			OutRelationSets[entityA] = AcquireHashSetFromPool();
 		}
+		OutRelationSets[entityA].Add(entityB);
 
-		public bool Has(Relation relation)
+		if (!InRelationSets.ContainsKey(entityB))
 		{
-			return indices.ContainsKey(relation);
+			InRelationSets[entityB] = AcquireHashSetFromPool();
 		}
+		InRelationSets[entityB].Add(entityA);
 
-		// FIXME: creating the new Relation in here is slightly deranged
-		public IEnumerable<(Entity, TRelation)> OutRelations(int entityID)
+		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))
 		{
-			if (outRelations.ContainsKey(entityID))
-			{
-				foreach (var id in outRelations[entityID])
-				{
-					var relation = new Relation(entityID, id);
-					yield return (relation.B, relationDatas[indices[relation]]);
-				}
-			}
+			return entityOutRelations.GetEnumerator();
 		}
-
-		public (Entity, TRelation) OutFirst(int entityID)
+		else
 		{
+			return ReverseSpanEnumerator<Entity>.Empty;
+		}
+	}
+
+	public Entity OutFirst(Entity Entity)
+	{
+		return OutNth(Entity, 0);
+	}
+
+	public Entity OutNth(Entity Entity, int n)
+	{
 #if DEBUG
-			if (!outRelations.ContainsKey(entityID))
-			{
-				throw new KeyNotFoundException("No out relations to this entity!");
-			}
+		if (!OutRelationSets.ContainsKey(Entity) || OutRelationSets[Entity].Count == 0)
+		{
+			throw new KeyNotFoundException("No out relations to this entity!");
+		}
 #endif
-			var relation = new Relation(entityID, outRelations[entityID][0]);
-			return (relation.B, relationDatas[indices[relation]]);
-		}
+		return OutRelationSets[Entity][n];
+	}
 
-		public bool HasOutRelation(int entityID)
-		{
-			return outRelations.ContainsKey(entityID) && outRelations[entityID].Count > 0;
-		}
+	public bool HasOutRelation(Entity Entity)
+	{
+		return OutRelationSets.ContainsKey(Entity) && OutRelationSets[Entity].Count > 0;
+	}
 
-		public int OutRelationCount(int entityID)
-		{
-			return outRelations.ContainsKey(entityID) ? outRelations[entityID].Count : 0;
-		}
+	public int OutRelationCount(Entity Entity)
+	{
+		return OutRelationSets.TryGetValue(Entity, out var entityOutRelations) ? entityOutRelations.Count : 0;
+	}
 
-		public IEnumerable<(Entity, TRelation)> InRelations(int entityID)
+	public ReverseSpanEnumerator<Entity> InRelations(Entity Entity)
+	{
+		if (InRelationSets.TryGetValue(Entity, out var entityInRelations))
 		{
-			if (inRelations.ContainsKey(entityID))
-			{
-				foreach (var id in inRelations[entityID])
-				{
-					var relation = new Relation(id, entityID);
-					yield return (relation.A, relationDatas[indices[relation]]);
-				}
-			}
+			return entityInRelations.GetEnumerator();
 		}
-
-		public (Entity, TRelation) InFirst(int entityID)
+		else
 		{
+			return ReverseSpanEnumerator<Entity>.Empty;
+		}
+	}
+
+	public Entity InFirst(Entity Entity)
+	{
+		return InNth(Entity, 0);
+	}
+
+	public Entity InNth(Entity Entity, int n)
+	{
 #if DEBUG
-			if (!inRelations.ContainsKey(entityID))
-			{
-				throw new KeyNotFoundException("No out relations to this entity!");
-			}
+		if (!InRelationSets.ContainsKey(Entity) || InRelationSets[Entity].Count == 0)
+		{
+			throw new KeyNotFoundException("No in relations to this entity!");
+		}
 #endif
 
-			var relation = new Relation(inRelations[entityID][0], entityID);
-			return (relation.A, relationDatas[indices[relation]]);
-		}
+		return InRelationSets[Entity][n];
+	}
 
-		public bool HasInRelation(int entityID)
-		{
-			return inRelations.ContainsKey(entityID) && inRelations[entityID].Count > 0;
-		}
+	public bool HasInRelation(Entity Entity)
+	{
+		return InRelationSets.ContainsKey(Entity) && InRelationSets[Entity].Count > 0;
+	}
 
-		public int InRelationCount(int entityID)
-		{
-			return inRelations.ContainsKey(entityID) ? inRelations[entityID].Count : 0;
-		}
+	public int InRelationCount(Entity Entity)
+	{
+		return InRelationSets.TryGetValue(Entity, out var entityInRelations) ? entityInRelations.Count : 0;
+	}
 
-		public bool Remove(Relation relation)
+	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))
 		{
-			if (outRelations.ContainsKey(relation.A.ID))
+			entityOutRelations.Remove(entityB);
+			if (OutRelationSets[entityA].Count == 0)
 			{
-				outRelations[relation.A.ID].Remove(relation.B.ID);
+				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;
 			}
 
-			if (inRelations.ContainsKey(relation.B.ID))
+			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)
 			{
-				inRelations[relation.B.ID].Remove(relation.A.ID);
+				Remove(entity, entityB);
 			}
 
-			if (indices.ContainsKey(relation))
-			{
-				var index = indices[relation];
-				var lastElementIndex = count - 1;
+			ReturnHashSetToPool(entityOutRelations);
+			OutRelationSets.Remove(entity);
+		}
 
-				// move an element into the hole
-				if (index != lastElementIndex)
+		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)
 				{
-					var lastRelation = relations[lastElementIndex];
-					indices[lastRelation] = index;
-					relationDatas[index] = relationDatas[lastElementIndex];
-					relations[index] = lastRelation;
+					set.Dispose();
 				}
 
-				count -= 1;
-				indices.Remove(relation);
-				return true;
+				Relations.Dispose();
+				RelationDatas.Dispose();
 			}
 
-			return false;
+			IsDisposed = true;
 		}
+	}
 
-		public void UnrelateAll(int entityID)
-		{
-			if (outRelations.ContainsKey(entityID))
-			{
-				foreach (var entityB in outRelations[entityID])
-				{
-					Remove(new Relation(entityID, entityB));
-				}
+	// ~RelationStorage()
+	// {
+	// 	// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
+	// 	Dispose(disposing: false);
+	// }
 
-				ReturnHashSetToPool(outRelations[entityID]);
-				outRelations.Remove(entityID);
-			}
-
-			if (inRelations.ContainsKey(entityID))
-			{
-				foreach (var entityA in inRelations[entityID])
-				{
-					Remove(new Relation(entityA, entityID));
-				}
-
-				ReturnHashSetToPool(inRelations[entityID]);
-				inRelations.Remove(entityID);
-			}
-		}
-
-		public override void OnEntityDestroy(int entityID)
-		{
-			UnrelateAll(entityID);
-		}
-
-		private IndexableSet<int> AcquireHashSetFromPool()
-		{
-			if (listPool.Count == 0)
-			{
-				listPool.Push(new IndexableSet<int>());
-			}
-
-			return listPool.Pop();
-		}
-
-		private void ReturnHashSetToPool(IndexableSet<int> hashSet)
-		{
-			hashSet.Clear();
-			listPool.Push(hashSet);
-		}
-
-		public override RelationStorageState CreateState()
-		{
-			return RelationStorageState.Create<TRelation>(count);
-		}
-
-		public override void Save(RelationStorageState state)
-		{
-			ReadOnlySpan<byte> relationBytes = MemoryMarshal.Cast<Relation, byte>(relations);
-
-			if (relationBytes.Length > state.Relations.Length)
-			{
-				Array.Resize(ref state.Relations, relationBytes.Length);
-			}
-			relationBytes.CopyTo(state.Relations);
-
-			ReadOnlySpan<byte> relationDataBytes = MemoryMarshal.Cast<TRelation, byte>(relationDatas);
-
-			if (relationDataBytes.Length > state.RelationDatas.Length)
-			{
-				Array.Resize(ref state.RelationDatas, relationDataBytes.Length);
-			}
-			relationDataBytes.CopyTo(state.RelationDatas);
-
-			state.Count = count;
-		}
-
-		public override void Load(RelationStorageState state)
-		{
-			state.Relations.CopyTo(MemoryMarshal.Cast<Relation, byte>(relations));
-			state.RelationDatas.CopyTo(MemoryMarshal.Cast<TRelation, byte>(relationDatas));
-
-			indices.Clear();
-			outRelations.Clear();
-			inRelations.Clear();
-			for (var i = 0; i < state.Count; i += 1)
-			{
-				var relation = relations[i];
-				indices[relation] = i;
-
-				if (!outRelations.ContainsKey(relation.A.ID))
-				{
-					outRelations[relation.A.ID] = AcquireHashSetFromPool();
-				}
-				outRelations[relation.A.ID].Add(relation.B.ID);
-
-				if (!inRelations.ContainsKey(relation.B.ID))
-				{
-					inRelations[relation.B.ID] = AcquireHashSetFromPool();
-				}
-				inRelations[relation.B.ID].Add(relation.A.ID);
-			}
-
-			count = state.Count;
-		}
+	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

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

src/Snapshot.cs

@@ -0,0 +1,378 @@
+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
+{
+	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)
+	{
+		// restore id assigner state
+		EntityIdAssigner.CopyTo(world.EntityIdAssigner);
+
+		// restore filter states
+		// this could be sped up if we figured out a direct IndexableSet copy
+		foreach (var (signature, entityList) in Filters)
+		{
+			var filter = world.FilterIndex[signature];
+
+			filter.Clear();
+
+			foreach (var entity in entityList)
+			{
+				filter.AddEntity(entity);
+			}
+		}
+
+		// 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)
+				{
+					Components.Dispose();
+					EntityIDs.Dispose();
+				}
+
+				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)
+			{
+				var relation = Relations.Get<(Entity, Entity)>(index);
+				relationStorage.Indices[relation] = index;
+
+				relationStorage.Indices[relation] = index;
+
+				if (!relationStorage.OutRelationSets.ContainsKey(relation.Item1))
+				{
+					relationStorage.OutRelationSets[relation.Item1] =
+						relationStorage.AcquireHashSetFromPool();
+				}
+
+				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)
+		{
+			if (!IsDisposed)
+			{
+				if (disposing)
+				{
+					Relations.Dispose();
+					RelationDatas.Dispose();
+				}
+
+				IsDisposed = true;
+			}
+		}
+
+		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 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();
+			}
+
+			IsDisposed = true;
+		}
+	}
+
+	public void Dispose()
+	{
+		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
+		Dispose(disposing: true);
+		GC.SuppressFinalize(this);
+	}
+}

src/State/ComponentDepotState.cs

@@ -1,11 +0,0 @@
-using System;
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-	internal class ComponentDepotState
-	{
-		public Dictionary<Type, ComponentStorageState> StorageStates = new Dictionary<Type, ComponentStorageState>();
-		public Dictionary<FilterSignature, IndexableSetState<int>> FilterStates = new Dictionary<FilterSignature, IndexableSetState<int>>();
-	}
-}

src/State/ComponentStorageState.cs

@@ -1,27 +0,0 @@
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-    internal class ComponentStorageState
-    {
-		public int Count;
-		public byte[] EntityIDs;
-		public byte[] Components;
-
-        public unsafe static ComponentStorageState Create<TComponent>(int count) where TComponent : unmanaged
-        {
-			return new ComponentStorageState(
-                count,
-                count * sizeof(int),
-                count * sizeof(TComponent)
-            );
-		}
-
-        private ComponentStorageState(int count, int entityIDSize, int componentSize)
-        {
-			Count = count;
-			EntityIDs = new byte[entityIDSize];
-			Components = new byte[componentSize];
-		}
-	}
-}

src/State/EntityStorageState.cs

@@ -1,10 +0,0 @@
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-    internal class EntityStorageState
-    {
-		public int NextID;
-		public List<int> availableIDs = new List<int>();
-	}
-}

src/State/IndexableSetState.cs

@@ -1,16 +0,0 @@
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-    internal class IndexableSetState<T> where T : unmanaged
-    {
-		public int Count;
-		public byte[] Array;
-
-        public unsafe IndexableSetState(int count)
-        {
-			Count = count;
-			Array = new byte[sizeof(T) * count];
-		}
-	}
-}

src/State/RelationDepotState.cs

@@ -1,10 +0,0 @@
-using System;
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-    internal class RelationDepotState
-    {
-		public Dictionary<Type, RelationStorageState> StorageStates = new Dictionary<Type, RelationStorageState>();
-	}
-}

src/State/RelationStorageState.cs

@@ -1,27 +0,0 @@
-using System.Collections.Generic;
-
-namespace MoonTools.ECS
-{
-	internal class RelationStorageState
-	{
-		public int Count;
-		public byte[] Relations;
-		public byte[] RelationDatas;
-
-		public unsafe static RelationStorageState Create<TRelation>(int count) where TRelation : unmanaged
-		{
-			return new RelationStorageState(
-				count,
-				count * sizeof(Relation),
-				count * sizeof(TRelation)
-			);
-		}
-
-		private RelationStorageState(int count, int relationSize, int relationDataSize)
-		{
-			Count = count;
-			Relations = new byte[relationSize];
-			RelationDatas = new byte[relationDataSize];
-		}
-	}
-}

src/State/WorldState.cs

@@ -1,16 +0,0 @@
-namespace MoonTools.ECS
-{
-    public class WorldState
-    {
-		internal readonly ComponentDepotState ComponentDepotState;
-		internal readonly EntityStorageState EntityStorageState;
-		internal readonly RelationDepotState RelationDepotState;
-
-		public WorldState()
-        {
-			ComponentDepotState = new ComponentDepotState();
-			EntityStorageState = new EntityStorageState();
-			RelationDepotState = new RelationDepotState();
-		}
-	}
-}

src/System.cs

@@ -1,94 +1,15 @@
 using System;
-using System.Collections.Generic;
 
-namespace MoonTools.ECS
+namespace MoonTools.ECS;
+
+public abstract class System : Manipulator
 {
-	public abstract class System : EntityComponentReader
-	{
-		internal MessageDepot MessageDepot => World.MessageDepot;
+	protected System(World world) : base(world) { }
 
-		public System(World world) : base(world) { }
+	public abstract void Update(TimeSpan delta);
 
-		public abstract void Update(TimeSpan delta);
-
-		protected Entity CreateEntity()
-		{
-			return EntityStorage.Create();
-		}
-
-		protected void Set<TComponent>(in Entity entity, in TComponent component) where TComponent : unmanaged
-		{
-#if DEBUG
-			// check for use after destroy
-			if (!Exists(entity))
-			{
-				throw new ArgumentException("This entity is not valid!");
-			}
-#endif
-			ComponentDepot.Set<TComponent>(entity.ID, component);
-		}
-
-		protected void Remove<TComponent>(in Entity entity) where TComponent : unmanaged
-		{
-			ComponentDepot.Remove<TComponent>(entity.ID);
-		}
-
-		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 IEnumerable<TMessage> ReadMessagesWithEntity<TMessage>(in Entity entity) where TMessage : unmanaged, IHasEntity
-		{
-			return MessageDepot.WithEntity<TMessage>(entity.ID);
-		}
-
-		protected ref readonly TMessage ReadMessageWithEntity<TMessage>(in Entity entity) where TMessage : unmanaged, IHasEntity
-		{
-			return ref MessageDepot.FirstWithEntity<TMessage>(entity.ID);
-		}
-
-		protected bool SomeMessageWithEntity<TMessage>(in Entity entity) where TMessage : unmanaged, IHasEntity
-		{
-			return MessageDepot.SomeWithEntity<TMessage>(entity.ID);
-		}
-
-		protected void Send<TMessage>(in TMessage message) where TMessage : unmanaged
-		{
-			MessageDepot.Add(message);
-		}
-
-		protected void Relate<TRelationKind>(in Entity entityA, in Entity entityB, TRelationKind relationData) where TRelationKind : unmanaged
-		{
-			RelationDepot.Set<TRelationKind>(new Relation(entityA, entityB), relationData);
-		}
-
-		protected void Unrelate<TRelationKind>(in Entity entityA, in Entity entityB) where TRelationKind : unmanaged
-		{
-			RelationDepot.Remove<TRelationKind>(new Relation(entityA, entityB));
-		}
-
-		protected void UnrelateAll<TRelationKind>(in Entity entity) where TRelationKind : unmanaged
-		{
-			RelationDepot.UnrelateAll<TRelationKind>(entity.ID);
-		}
-
-		// FIXME: this is insanely inefficient
-		protected void Destroy(in Entity entity)
-		{
-			ComponentDepot.OnEntityDestroy(entity.ID);
-			RelationDepot.OnEntityDestroy(entity.ID);
-			EntityStorage.Destroy(entity);
-		}
-	}
+	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);
 }

src/TypeId.cs

@@ -0,0 +1,82 @@
+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/World.cs

@@ -1,54 +1,506 @@
-namespace MoonTools.ECS
+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
 {
-	public class World
+#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>();
+#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
 	{
-		internal readonly EntityStorage EntityStorage = new EntityStorage();
-		internal readonly ComponentDepot ComponentDepot = new ComponentDepot();
-		internal readonly MessageDepot MessageDepot = new MessageDepot();
-		internal readonly RelationDepot RelationDepot = new RelationDepot();
-
-		public Entity CreateEntity()
+		var typeId = new TypeId(ComponentTypeIdAssigner<T>.Id);
+		if (typeId < ComponentIndex.Count)
 		{
-			return EntityStorage.Create();
+			return typeId;
 		}
 
-		public void Set<TComponent>(Entity entity, in TComponent component) where TComponent : unmanaged
+		// add missing storages, it's possible for there to be multiples in multi-world scenarios
+		for (var i = ComponentIndex.Count; i <= typeId; i += 1)
 		{
-			ComponentDepot.Set(entity.ID, component);
+			var missingTypeId = new TypeId((uint) i);
+			var componentStorage = new ComponentStorage(missingTypeId, ComponentTypeElementSizes[i]);
+			ComponentIndex.Add(componentStorage);
+			ComponentTypeToFilter.Add(new List<Filter>());
 		}
 
-		public void Send<TMessage>(in TMessage message) where TMessage : unmanaged
+		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))
 		{
-			MessageDepot.Add(message);
+			filter = new Filter(this, signature);
+
+			foreach (var typeId in signature.Included)
+			{
+				ComponentTypeToFilter[(int) typeId.Value].Add(filter);
+			}
+
+			foreach (var typeId in signature.Excluded)
+			{
+				ComponentTypeToFilter[(int) typeId.Value].Add(filter);
+			}
+
+			FilterIndex.Add(signature, filter);
 		}
 
-		public void FinishUpdate()
+		return filter;
+	}
+
+	// ENTITIES
+
+	public Entity CreateEntity(string tag = "")
+	{
+		var entity = new Entity(EntityIdAssigner.Assign());
+
+		if (entity.ID == EntityComponentIndex.Count)
 		{
-			MessageDepot.Clear();
+			EntityRelationIndex.Add(new IndexableSet<TypeId>());
+			EntityComponentIndex.Add(new IndexableSet<TypeId>());
+			EntityTags.Add(tag);
 		}
 
-		public void DisableSerialization<TComponent>() where TComponent : unmanaged
+		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)
 		{
-			ComponentDepot.DisableSerialization<TComponent>();
+			var componentStorage = ComponentIndex[componentTypeIndex];
+			componentStorage.Remove(entity);
+
+			foreach (var filter in ComponentTypeToFilter[componentTypeIndex])
+			{
+				filter.RemoveEntity(entity);
+			}
 		}
 
-		public WorldState CreateState()
+		// remove all relations from storage
+		foreach (var relationTypeIndex in relationSet)
 		{
-			return new WorldState();
+			var relationStorage = RelationIndex[relationTypeIndex];
+			relationStorage.RemoveEntity(entity);
 		}
 
-		public void Save(WorldState state)
-		{
-			ComponentDepot.Save(state.ComponentDepotState);
-			EntityStorage.Save(state.EntityStorageState);
-			RelationDepot.Save(state.RelationDepotState);
-		}
+		componentSet.Clear();
+		relationSet.Clear();
 
-		public void Load(WorldState state)
+		// 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))
 		{
-			ComponentDepot.Load(state.ComponentDepotState);
-			EntityStorage.Load(state.EntityStorageState);
-			RelationDepot.Load(state.RelationDepotState);
+			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();
+			}
+
+			IsDisposed = true;
+		}
+	}
+
+	// // 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);
+	}
 }