src/ComponentDepot.cs

@@ -10,11 +10,18 @@ internal class ComponentDepot
 
 	private Dictionary<int, HashSet<Type>> entityComponentMap = new Dictionary<int, HashSet<Type>>();
 
+	#if DEBUG
+	private Dictionary<Type, Filter> singleComponentFilters = new Dictionary<Type, Filter>();
+	#endif
+
 	internal void Register<TComponent>() where TComponent : struct
 	{
 		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
 		}
 	}
 
@@ -79,14 +86,9 @@ internal class ComponentDepot
 		}
 	}
 
-	public ref readonly Entity GetEntity<TComponent>() where TComponent : struct
+	public Entity GetSingletonEntity<TComponent>() where TComponent : struct
 	{
-		return ref Lookup<TComponent>().FirstEntity();
+		return Lookup<TComponent>().FirstEntity();
-	}
-
-	public ReadOnlySpan<Entity> ReadEntities<TComponent>() where TComponent : struct
-	{
-		return Lookup<TComponent>().AllEntities();
 	}
 
 	public ReadOnlySpan<TComponent> ReadComponents<TComponent>() where TComponent : struct
@@ -226,8 +228,7 @@ internal class ComponentDepot
 		filterSignatureToEntityIDs[filterSignature].Add(entityID);
 	}
 
-	// debug use only!
+	#if DEBUG
-
 	public IEnumerable<object> Debug_GetAllComponents(int entityID)
 	{
 		foreach (var (type, storage) in storages)
@@ -239,9 +240,9 @@ internal class ComponentDepot
 		}
 	}
 
-	public ReadOnlySpan<Entity> Debug_GetEntities(Type componentType)
+	public IEnumerable<Entity> Debug_GetEntities(Type componentType)
 	{
-		return Lookup(componentType).AllEntities();
+		return singleComponentFilters[componentType].Entities;
 	}
 
 	public IEnumerable<Type> Debug_SearchComponentType(string typeString)
@@ -254,4 +255,5 @@ internal class ComponentDepot
 			}
 		}
 	}
+	#endif
 }

src/ComponentStorage.cs

@@ -4,8 +4,6 @@ internal abstract class ComponentStorage
 {
 	public abstract bool Has(int entityID);
 	public abstract void Remove(int entityID);
-	public abstract ReadOnlySpan<Entity> AllEntities();
-
 	public abstract object Debug_Get(int entityID);
 }
 
@@ -13,10 +11,9 @@ internal abstract class ComponentStorage
 internal class ComponentStorage<TComponent> : ComponentStorage where TComponent : struct
 {
 	private int nextID;
-	private IDStorage idStorage = new IDStorage();
+	private readonly Dictionary<int, int> entityIDToStorageIndex = new Dictionary<int, int>(16);
-	private readonly Dictionary<int, int> entityIDToStorageIndex = new Dictionary<int, int>();
+	private int[] entityIDs = new int[16];
-	private Entity[] storageIndexToEntities = new Entity[64];
+	private TComponent[] components = new TComponent[16];
-	private TComponent[] components = new TComponent[64];
 
 	public bool Any()
 	{
@@ -59,11 +56,11 @@ internal class ComponentStorage<TComponent> : ComponentStorage where TComponent
 			if (index >= components.Length)
 			{
 				Array.Resize(ref components, components.Length * 2);
-				Array.Resize(ref storageIndexToEntities, storageIndexToEntities.Length * 2);
+				Array.Resize(ref entityIDs, entityIDs.Length * 2);
 			}
 
 			entityIDToStorageIndex[entityID] = index;
-			storageIndexToEntities[index] = new Entity(entityID);
+			entityIDs[index] = entityID;
 		}
 
 		components[entityIDToStorageIndex[entityID]] = component;
@@ -79,13 +76,12 @@ internal class ComponentStorage<TComponent> : ComponentStorage where TComponent
 			var lastElementIndex = nextID - 1;
 
 			// move a component into the hole to maintain contiguous memory
-			if (entityIDToStorageIndex.Count > 0 && storageIndex != lastElementIndex)
+			if (lastElementIndex != storageIndex)
 			{
-				var lastEntity = storageIndexToEntities[lastElementIndex];
+				var lastEntityID = entityIDs[lastElementIndex];
-
+				entityIDToStorageIndex[lastEntityID] = storageIndex;
-				entityIDToStorageIndex[lastEntity.ID] = storageIndex;
-				storageIndexToEntities[storageIndex] = lastEntity;
 				components[storageIndex] = components[lastElementIndex];
+				entityIDs[storageIndex] = lastEntityID;
 			}
 
 			nextID -= 1;
@@ -98,18 +94,13 @@ internal class ComponentStorage<TComponent> : ComponentStorage where TComponent
 		entityIDToStorageIndex.Clear();
 	}
 
-	public override ReadOnlySpan<Entity> AllEntities()
-	{
-		return new ReadOnlySpan<Entity>(storageIndexToEntities, 0, nextID);
-	}
-
 	public ReadOnlySpan<TComponent> AllComponents()
 	{
 		return new ReadOnlySpan<TComponent>(components, 0, nextID);
 	}
 
-	public ref readonly Entity FirstEntity()
+	public Entity FirstEntity()
 	{
-		return ref storageIndexToEntities[0];
+		return new Entity(entityIDs[0]);
 	}
 }

src/DebugSystem.cs

@@ -1,5 +1,7 @@
 // NOTE: these methods are very inefficient
 // this class should only be used in debugging contexts!!
+
+#if DEBUG
 namespace MoonTools.ECS
 {
 	public abstract class DebugSystem : System
@@ -13,7 +15,7 @@ namespace MoonTools.ECS
 			return ComponentDepot.Debug_GetAllComponents(entity.ID);
 		}
 
-		protected ReadOnlySpan<Entity> Debug_GetEntities(Type componentType)
+		protected IEnumerable<Entity> Debug_GetEntities(Type componentType)
 		{
 			return ComponentDepot.Debug_GetEntities(componentType);
 		}
@@ -24,3 +26,4 @@ namespace MoonTools.ECS
 		}
 	}
 }
+#endif

src/EntityComponentReader.cs

@@ -16,12 +16,6 @@ public abstract class EntityComponentReader
 		ComponentDepot = componentDepot;
 	}
 
-	// TODO: is this faster or slower than a single-component Filter?
-	protected ReadOnlySpan<Entity> ReadEntities<TComponent>() where TComponent : struct
-	{
-		return ComponentDepot.ReadEntities<TComponent>();
-	}
-
 	protected ReadOnlySpan<TComponent> ReadComponents<TComponent>() where TComponent : struct
 	{
 		return ComponentDepot.ReadComponents<TComponent>();
@@ -47,9 +41,9 @@ public abstract class EntityComponentReader
 		return ref ComponentDepot.Get<TComponent>();
 	}
 
-	protected ref readonly Entity GetEntity<TComponent>() where TComponent : struct
+	protected Entity GetSingletonEntity<TComponent>() where TComponent : struct
 	{
-		return ref ComponentDepot.GetEntity<TComponent>();
+		return ComponentDepot.GetSingletonEntity<TComponent>();
 	}
 
 	protected bool Exists(in Entity entity)