add LinkComponentIndex<> - made IndexExtensions.GetAllLinkedEntities(…

…) obsolete

src/ECS/Index/ComponentIndex.cs

@@ -39,25 +39,5 @@ internal ComponentIndex(AbstractComponentIndex<TValue> index) {
     /// </remarks>
     public IReadOnlyCollection<TValue> Values => index.IndexedComponentValues;
 
-    /// <summary>
-    /// Returns all entities linked by the specified <see cref="ILinkComponent"/> type.<br/>
-    /// Executes in O(1). Each entity in the returned list is unique. See remarks for additional infos.
-    /// </summary>
-    /// <remarks>
-    /// <list type="bullet">
-    ///   <item>
-    ///     The returned collection changes when component link values are updated, removed or added.
-    ///   </item>
-    ///   <item>
-    ///     To get the entities linking a specific entity use <see cref="IndexExtensions.GetIncomingLinks{TComponent}"/>.<br/>
-    ///   </item>
-    ///   <item>
-    ///     The method is a specialized version of <see cref="Values"/><br/>
-    ///     using <c> TIndexedComponent = ILinkComponent</c> and <c>TValue = Entity</c>.  
-    ///   </item>
-    /// </list>
-    /// </remarks>
-    public IReadOnlyCollection<Entity> LinkedEntities => ((AbstractComponentIndex<Entity>)(object)index).IndexedComponentValues;
-
     public override string ToString() => $"Count: {Values.Count}";
-}
+}

src/ECS/Index/ILinkComponent.cs

@@ -20,7 +20,7 @@ namespace Friflo.Engine.ECS;
 ///   </item>
 ///   <item>
 ///     Return all entities linked by a specific <see cref="ILinkComponent"/> type.<br/>
-///     See <see cref="IndexExtensions.GetAllLinkedEntities{TComponent}"/>
+///     See <see cref="LinkComponentIndex{TLinkComponent}.Values"/>
 ///   </item>
 ///   <item>
 ///     Filter entities in a query having a <see cref="ILinkComponent"/> to a specific entity.<br/>

src/ECS/Index/IndexExtensions.cs

@@ -40,6 +40,17 @@ public static ComponentIndex<TIndexedComponent,TValue> ComponentIndex<TIndexedCo
         var index = (AbstractComponentIndex<TValue>)StoreIndex.GetIndex(store, StructInfo<TIndexedComponent>.Index);
         return new ComponentIndex<TIndexedComponent, TValue>(index);
     }
+
+    /// <summary>
+    /// Returns the index for link components to search entities with a specific entity in O(1).<br/>
+    /// Executes in O(1). 
+    /// </summary>
+    public static LinkComponentIndex<TLinkComponent> LinkComponentIndex<TLinkComponent>(this EntityStore store)
+        where TLinkComponent: struct, ILinkComponent
+    {
+        var index = (AbstractComponentIndex<Entity>)StoreIndex.GetIndex(store, StructInfo<TLinkComponent>.Index);
+        return new LinkComponentIndex<TLinkComponent>(index);
+    }
 
     /// <summary>
     /// Obsolete: Use <see cref="ComponentIndex{TIndexedComponent,TValue}.this[TValue]"/><br/>
@@ -82,7 +93,7 @@ public static  IReadOnlyCollection<TValue> GetAllIndexedComponentValues<TCompone
     }
 
     /// <summary>
-    /// Obsolete: Use <see cref="ComponentIndex{TIndexedComponent,TValue}.LinkedEntities"/><br/>
+    /// Obsolete: Use <see cref="LinkComponentIndex{TLinkComponent}.Values"/><br/>
     /// Returns all entities linked by the specified <see cref="ILinkComponent"/> type.<br/>
     /// Executes in O(1). Each entity in the returned list is unique. See remarks for additional infos.
     /// </summary>
@@ -100,6 +111,7 @@ public static  IReadOnlyCollection<TValue> GetAllIndexedComponentValues<TCompone
     ///   </item>
     /// </list>
     /// </remarks>
+    [Obsolete("replace with property: LinkComponentIndex<TLinkComponent>().Values")]
     public static IReadOnlyCollection<Entity> GetAllLinkedEntities<TComponent>(this EntityStore store)
         where TComponent: struct, ILinkComponent
     {

src/ECS/Index/LinkComponentIndex.cs

@@ -0,0 +1,39 @@
+using System.Collections.Generic;
+using Friflo.Engine.ECS.Index;
+
+// ReSharper disable once CheckNamespace
+namespace Friflo.Engine.ECS;
+
+public readonly struct LinkComponentIndex <TLinkComponent>
+    where TLinkComponent: struct, ILinkComponent
+{
+    private readonly AbstractComponentIndex<Entity> index;
+
+    internal LinkComponentIndex(AbstractComponentIndex<Entity> index) {
+        this.index = index;
+    }
+
+    /// <summary>
+    /// Return the entities having a link component with the passed component value.<br/>
+    /// Executes in O(1) with default index. 
+    /// </summary>
+    public Entities this[Entity value] => index.GetHasValueEntities(value);
+
+    /// <summary>
+    /// Returns all indexed link component values of the passed<see cref="Entity"/> type.<br/>
+    /// Executes in O(1). Each value in the returned list is unique. See remarks for additional infos.
+    /// </summary>
+    /// <remarks>
+    /// <list type="bullet">
+    ///   <item>
+    ///     The returned collection changes when indexed component values are updated, removed or added.
+    ///   </item>
+    ///   <item>
+    ///     To get the entities having a specific component value use <see cref="this[Entity]"/>.
+    ///   </item>
+    /// </list>
+    /// </remarks>
+    public IReadOnlyCollection<Entity> Values => index.IndexedComponentValues;
+
+    public override string ToString() => $"Count: {Values.Count}";
+}

src/Tests/ECS/Index/Test_Index.cs

@@ -105,6 +105,7 @@ public static void Test_Index_Component_Update()
     public static void Test_Index_indexed_Entity()
     {
         var store   = new EntityStore();
+        var index   = store.LinkComponentIndex<LinkComponent>();
         var entity1 = store.CreateEntity(1);
         var entity2 = store.CreateEntity(2);
         var entity3 = store.CreateEntity(3);
@@ -113,11 +114,14 @@ public static void Test_Index_indexed_Entity()
         var target5 = store.CreateEntity(5);
         var target6 = store.CreateEntity(6);
 
-        var values = store.GetAllLinkedEntities<LinkComponent>();
+        var values = index.Values;
 
         entity1.AddComponent(new LinkComponent { entity = target4 });   AreEqual(1, values.Count);
         entity2.AddComponent(new LinkComponent { entity = target5 });   AreEqual(2, values.Count);
         entity3.AddComponent(new LinkComponent { entity = target5 });   AreEqual(2, values.Count);
+
+        AreEqual(1, index[target4].Count);
+        AreEqual(2, index[target5].Count);
 
         int count = 0;
         foreach (var entity in values) {