ECS - add readonly struct IdRevision

src/ECS/Entity.cs

@@ -371,7 +371,7 @@ public     ref readonly Tags                Tags { get {
     /// <summary>Unique entity id.<br/>
     /// Uniqueness relates to the <see cref="Entity"/>'s stored in its <see cref="EntityStore"/></summary>
     [Browse(Never)]
-    [FieldOffset(8)]    internal    readonly    long        idRevision; // (8) - 4 (Id) + 2 (Revision) + 2 (padding)
+    [FieldOffset(8)]    internal    readonly    IdRevision  idRevision; // (8)
     // ReSharper disable once InconsistentNaming
     [FieldOffset(8)]    public      readonly    int         Id;         //  4
     [Browse(Never)]

src/ECS/Entity/IdRevision.cs

@@ -0,0 +1,32 @@
+// Copyright (c) Ullrich Praetz - https://github.com/friflo. All rights reserved.
+// See LICENSE file in the project root for full license information.
+
+using System;
+using System.Runtime.InteropServices;
+using static System.Diagnostics.DebuggerBrowsableState;
+using Browse = System.Diagnostics.DebuggerBrowsableAttribute;
+
+// ReSharper disable once CheckNamespace
+namespace Friflo.Engine.ECS;
+
+[StructLayout(LayoutKind.Explicit)]
+internal readonly struct IdRevision  : IEquatable<IdRevision>
+{
+    [FieldOffset(0)]    public   readonly   int     Id;         //  4
+    [FieldOffset(4)]    public   readonly   short   Revision;   //  2
+
+    [Browse(Never)]
+    [FieldOffset(0)]    internal readonly   long    value;      // (8) - 4 (Id) + 2 (Revision) + 2 (padding)
+
+    public          bool    Equals      (IdRevision other)              => value == other.value;
+    public static   bool    operator == (IdRevision a, IdRevision b)    => a.value == b.value;
+    public static   bool    operator != (IdRevision a, IdRevision b)    => a.value != b.value;
+
+    public override bool    Equals(object obj)  => throw new NotImplementedException("by intenetion to avoid boxing");
+    public override int     GetHashCode()       => Id ^ Revision;
+
+    internal IdRevision(int id, short revision) {
+        Id          = id;
+        Revision    = revision;
+    }
+}

src/Tests-internal/ECS/Test_Entity.cs

@@ -1,6 +1,9 @@
+using System;
+using System.Collections.Generic;
 using Friflo.Engine.ECS;
 using NUnit.Framework;
 using Tests.ECS;
+using Tests.Utils;
 using static NUnit.Framework.Assert;
 
 // ReSharper disable RedundantTypeDeclarationBody
@@ -9,6 +12,32 @@ namespace Internal.ECS {
 
 public static class Test_Entity
 {
+    [Test]
+    public static void Test_Entity_IdRevision()
+    {
+        var dict = new Dictionary<IdRevision, int>();
+        var idRef11 = new IdRevision(1,1);
+        var idRef21 = new IdRevision(2,1);
+
+        IsTrue(idRef11 == idRef11);
+        IsTrue(idRef11 != idRef21);
+
+        dict.Add(idRef11, 11);
+        dict.Add(idRef21, 21);
+
+        AreEqual(2,     dict.Count);
+        AreEqual(11,    dict[new IdRevision(1,1)]);
+
+        var start = Mem.GetAllocatedBytes();
+        _ = dict[new IdRevision(1,1)];
+        Mem.AssertNoAlloc(start);
+
+        Throws<NotImplementedException>(() => {
+            object obj = idRef11;
+            _ = obj.Equals(idRef11);
+        });
+    }
+
     [Test]
     public static void Test_Entity_Components()
     {