integer IDs and entity capacity

encompass-cs/Entity.cs

@@ -8,21 +8,16 @@ namespace Encompass
     /// </summary>
     public struct Entity : IEquatable<Entity>
     {
-        public readonly Guid ID;
+        public readonly int ID;
 
-        internal Entity(Guid id)
+        internal Entity(int id)
         {
             ID = id;
         }
 
         public override bool Equals(object obj)
         {
-            if (obj is Entity entity)
-            {
-                return Equals(entity);
-            }
-
-            return false;
+            return obj is Entity entity && Equals(entity);
         }
 
         public bool Equals(Entity other)

encompass-cs/EntityManager.cs

@@ -1,30 +1,45 @@
-using System;
-using System.Collections.Generic;
+using System.Collections.Generic;
+using Encompass.Exceptions;
 
 namespace Encompass
 {
     internal class EntityManager
     {
-        private readonly HashSet<Guid> IDs = new HashSet<Guid>();
+        private readonly int entityCapacity;
+        private readonly IDManager idManager = new IDManager();
+        private readonly HashSet<int> IDs = new HashSet<int>();
 
         private readonly HashSet<Entity> entitiesMarkedForDestroy = new HashSet<Entity>();
 
         private readonly ComponentManager componentManager;
 
-        public EntityManager(ComponentManager componentManager)
+        public EntityManager(ComponentManager componentManager, int entityCapacity)
         {
             this.componentManager = componentManager;
+            this.entityCapacity = entityCapacity;
+        }
+
+        private int NextID()
+        {
+            return idManager.NextID();
         }
 
         public Entity CreateEntity()
         {
-            var id = NextID();
-            var entity = new Entity(id);
-            IDs.Add(id);
-            return entity;
+            if (IDs.Count < entityCapacity)
+            {
+                var id = NextID();
+                var entity = new Entity(id);
+                IDs.Add(id);
+                return entity;
+            }
+            else
+            {
+                throw new EntityOverflowException("The number of entities has exceeded the entity capacity of {0}", entityCapacity);
+            }
         }
 
-        public bool EntityExists(Guid id)
+        public bool EntityExists(int id)
         {
             return IDs.Contains(id);
         }
@@ -40,14 +55,10 @@ namespace Encompass
             {
                 componentManager.MarkAllComponentsOnEntityForRemoval(entity);
                 IDs.Remove(entity.ID);
+                idManager.Free(entity.ID);
             }
 
             entitiesMarkedForDestroy.Clear();
         }
-
-        private Guid NextID()
-        {
-            return Guid.NewGuid();
-        }
     }
 }

encompass-cs/Exceptions/EntityOverflowException.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace Encompass.Exceptions
+{
+    public class EntityOverflowException : Exception
+    {
+        public EntityOverflowException(
+            string format,
+            params object[] args
+        ) : base(string.Format(format, args)) { }
+    }
+}

encompass-cs/IDManager.cs

@@ -0,0 +1,28 @@
+using System.Collections.Generic;
+
+namespace Encompass
+{
+    internal class IDManager
+    {
+        int nextID = 0;
+
+        private Stack<int> availableIDs = new Stack<int>();
+
+        public int NextID()
+        {
+            if (availableIDs.Count > 0)
+            {
+                return availableIDs.Pop();
+            }
+            else
+            {
+                return nextID++;
+            }
+        }
+
+        public void Free(int ID)
+        {
+            availableIDs.Push(ID);
+        }
+    }
+}

encompass-cs/WorldBuilder.cs

@@ -18,6 +18,7 @@ namespace Encompass
     /// </remarks>
     public class WorldBuilder
     {
+        private readonly int entityCapacity;
         private readonly List<Engine> engines = new List<Engine>();
         private readonly DirectedGraph<Engine, Unit> engineGraph = GraphBuilder.DirectedGraph<Engine>();
         private readonly ComponentStore startingComponentStoreForComponentManager = new ComponentStore();
@@ -39,14 +40,15 @@ namespace Encompass
 
         private readonly HashSet<Type> messageTypes = new HashSet<Type>();
 
-        public WorldBuilder()
+        public WorldBuilder(int entityCapacity = 32768)
         {
+            this.entityCapacity = entityCapacity;
             drawLayerManager = new DrawLayerManager();
             timeManager = new TimeManager();
             componentUpdateManager = new ComponentUpdateManager();
             componentManager = new ComponentManager(drawLayerManager, componentUpdateManager);
             messageManager = new MessageManager(timeManager);
-            entityManager = new EntityManager(componentManager);
+            entityManager = new EntityManager(componentManager, entityCapacity);
             renderManager = new RenderManager(drawLayerManager);
         }
 
@@ -402,7 +404,7 @@ namespace Encompass
             var dummyDrawLayerManager = new DrawLayerManager();
             var dummyComponentUpdateManager = new ComponentUpdateManager();
             var dummyComponentManager = new ComponentManager(dummyDrawLayerManager, dummyComponentUpdateManager);
-            var dummyEntityManager = new EntityManager(dummyComponentManager);
+            var dummyEntityManager = new EntityManager(dummyComponentManager, entityCapacity);
             var dummyRenderManager = new RenderManager(dummyDrawLayerManager);
 
             var prepEngineOrder = new List<Engine>();

test/EntityTest.cs

@@ -2,6 +2,7 @@ using NUnit.Framework;
 using FluentAssertions;
 
 using Encompass;
+using Encompass.Exceptions;
 
 namespace Tests
 {
@@ -20,5 +21,18 @@ namespace Tests
             Assert.AreEqual(entity, entity);
             Assert.IsTrue(entity == copyEntity);
         }
+
+        [Test]
+        public void EntityOverflowException()
+        {
+            var worldBuilder = new WorldBuilder(16);
+
+            for (var i = 0; i < 16; i++)
+            {
+                worldBuilder.CreateEntity();
+            }
+
+            Assert.Throws<EntityOverflowException>(() => worldBuilder.CreateEntity());
+        }
     }
 }