adds some convenience methods and doc comments

encompass-cs/ComponentMessageManager.cs

@@ -12,7 +12,7 @@ namespace Encompass
         private readonly Dictionary<Guid, Type> componentIDToType = new Dictionary<Guid, Type>();
 
         private readonly Dictionary<Guid, Guid> componentIDToEntityID = new Dictionary<Guid, Guid>();
-        
+
         private readonly Dictionary<Type, HashSet<Guid>> componentMessageTypeToExistingComponentIDs = new Dictionary<Type, HashSet<Guid>>();
         private readonly Dictionary<Type, HashSet<Guid>> componentMessageTypeToPendingComponentIDs = new Dictionary<Type, HashSet<Guid>>();
         private readonly Dictionary<Type, HashSet<Guid>> componentMessageTypeToComponentIDs = new Dictionary<Type, HashSet<Guid>>();
@@ -136,12 +136,12 @@ namespace Encompass
             }
         }
 
-        private void RegisterExistingOrPendingComponentMessage<TComponent>(Entity entity, Guid componentID, TComponent component) where TComponent: struct, IComponent
+        private void RegisterExistingOrPendingComponentMessage<TComponent>(Entity entity, Guid componentID, TComponent component) where TComponent : struct, IComponent
         {
             componentIDToComponent[componentID] = component;
             componentIDToEntityID[componentID] = entity.ID;
             componentIDToType[componentID] = typeof(TComponent);
-            
+
             if (!componentMessageTypeToComponentIDs.ContainsKey(typeof(TComponent)))
             {
                 componentMessageTypeToComponentIDs.Add(typeof(TComponent), new HashSet<Guid>());
@@ -163,7 +163,7 @@ namespace Encompass
             return Enumerable.Empty<(Guid, TComponent)>();
         }
 
-        internal IEnumerable<(Guid, TComponent)> ReadExistingComponentsByType<TComponent>() where TComponent: struct, IComponent
+        internal IEnumerable<(Guid, TComponent)> ReadExistingComponentsByType<TComponent>() where TComponent : struct, IComponent
         {
             if (componentMessageTypeToExistingComponentIDs.TryGetValue(typeof(TComponent), out HashSet<Guid> idSet))
             {
@@ -187,16 +187,19 @@ namespace Encompass
 
         internal (Guid, TComponent) ReadFirstExistingOrPendingComponentByType<TComponent>() where TComponent : struct, IComponent
         {
+            if (!SomeExistingOrPendingComponent<TComponent>()) { throw new Exceptions.NoComponentOfTypeException($"No Component with type {typeof(TComponent)} exists"); }
             return ReadExistingAndPendingComponentsByType<TComponent>().First();
         }
 
         internal (Guid, TComponent) ReadFirstExistingComponentByType<TComponent>() where TComponent : struct, IComponent
         {
+            if (!SomeExistingComponent<TComponent>()) { throw new Exceptions.NoComponentOfTypeException($"No Component with type {typeof(TComponent)} exists"); }
             return ReadExistingComponentsByType<TComponent>().First();
         }
 
         internal (Guid, TComponent) ReadFirstPendingComponentByType<TComponent>() where TComponent : struct, IComponent
         {
+            if (!SomeExistingComponent<TComponent>()) { throw new Exceptions.NoComponentOfTypeException($"No Component with type {typeof(TComponent)} exists"); }
             return ReadPendingComponentsByType<TComponent>().First();
         }
 

encompass-cs/Engine.cs

@@ -6,6 +6,11 @@ using Encompass.Exceptions;
 
 namespace Encompass
 {
+    /// <summary>
+    /// Engines are the Encompass notion of an ECS System.
+    /// They are responsible for reading the World state, reading messages, emitting messages, and creating or mutating Entities and Components.
+    /// Engines run once per World Update.
+    /// </summary>
     public abstract class Engine
     {
         internal readonly HashSet<Type> sendTypes = new HashSet<Type>();
@@ -77,23 +82,42 @@ namespace Encompass
             this.componentMessageManager = componentMessageManager;
         }
 
+        /// <summary>
+        /// Runs once per World update with the calculated delta-time.
+        /// </summary>
+        /// <param name="dt">The time in seconds that has elapsed since the previous frame.</param>
         public abstract void Update(double dt);
 
+        /// <summary>
+        /// Creates and returns a new empty Entity.
+        /// </summary>
         protected Entity CreateEntity()
         {
             return entityManager.CreateEntity();
         }
 
+        /// <summary>
+        /// Returns true if an Entity with the specified ID exists.
+        /// </summary>
         protected bool EntityExists(Guid entityID)
         {
             return entityManager.EntityExists(entityID);
         }
 
+        /// <summary>
+        /// Returns the Entity with the specified ID.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.EntityNotFoundException">
+        /// Thrown when an Entity with the given ID does not exist.
+        /// </exception>
         protected Entity GetEntity(Guid entityID)
         {
             return entityManager.GetEntity(entityID);
         }
 
+        /// <summary>
+        /// Returns the Entity ID associated with the specified Component Type and ID.
+        /// </summary>
         protected Guid GetEntityIDByComponentID<TComponent>(Guid componentID) where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
@@ -107,11 +131,37 @@ namespace Encompass
             return componentMessageManager.GetEntityIDByComponentID(componentID);
         }
 
+        /// <summary>
+        /// Returns the Entity associated with the specified Component Type and ID.
+        /// </summary>
         protected Entity GetEntityByComponentID<TComponent>(Guid componentID) where TComponent : struct, IComponent
         {
             return GetEntity(GetEntityIDByComponentID<TComponent>(componentID));
         }
 
+        /// <summary>
+        /// Returns an Entity containing the specified Component type. 
+        /// </summary>
+        protected Entity ReadEntity<TComponent>() where TComponent : struct, IComponent
+        {
+            var (id, component) = ReadComponent<TComponent>();
+            return GetEntityByComponentID<TComponent>(id);
+        }
+
+        /// <summary>
+        /// Returns all Entities containing the specified Component type. 
+        /// </summary>
+        protected IEnumerable<Entity> ReadEntities<TComponent>() where TComponent : struct, IComponent
+        {
+            foreach (var (id, component) in ReadComponents<TComponent>())
+            {
+                yield return GetEntityByComponentID<TComponent>(id);
+            }
+        }
+
+        /// <summary>
+        /// Returns the Component struct with the specified Component Type and ID.
+        /// </summary>
         protected TComponent GetComponentByID<TComponent>(Guid componentID) where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
@@ -142,7 +192,10 @@ namespace Encompass
             return GetEntity(componentManager.GetEntityIDByComponentID(componentID));
         }
 
-        protected IEnumerable<ValueTuple<Guid, TComponent>> ReadComponents<TComponent>() where TComponent : struct, IComponent
+        /// <summary>
+        /// Returns all of the Components with the specified Component Type.
+        /// </summary>
+        protected IEnumerable<(Guid, TComponent)> ReadComponents<TComponent>() where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
             var existingRead = receiveTypes.Contains(typeof(ComponentMessage<TComponent>));
@@ -164,7 +217,10 @@ namespace Encompass
             }
         }
 
-        protected ValueTuple<Guid, TComponent> ReadComponent<TComponent>() where TComponent : struct, IComponent
+        /// <summary>
+        /// Returns a Component with the specified Component Type and ID. If multiples exist, an arbitrary Component is returned. 
+        /// </summary>
+        protected (Guid, TComponent) ReadComponent<TComponent>() where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
             var existingRead = receiveTypes.Contains(typeof(ComponentMessage<TComponent>));
@@ -186,6 +242,9 @@ namespace Encompass
             }
         }
 
+        /// <summary>
+        /// Returns true if any Component with the specified Component Type exists.
+        /// </summary>
         protected bool SomeComponent<TComponent>() where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
@@ -208,7 +267,16 @@ namespace Encompass
             }
         }
 
-        protected ValueTuple<Guid, TComponent> GetComponent<TComponent>(Entity entity) where TComponent : struct, IComponent
+        /// <summary>
+        /// Returns a Component with the specified Type that exists on the Entity.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.NoComponentOfTypeOnEntityException">
+        /// Thrown when the Entity does not have a Component of the specified Type
+        /// </exception>
+        /// <exception cref="Encompass.Exceptions.IllegalReadException">
+        /// Thrown when the Engine does not declare that it reads the given Component Type.
+        /// </exception>
+        protected (Guid, TComponent) GetComponent<TComponent>(Entity entity) where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
             var existingRead = receiveTypes.Contains(typeof(ComponentMessage<TComponent>));
@@ -241,6 +309,12 @@ namespace Encompass
             }
         }
 
+        /// <summary>
+        /// Returns true if the Entity has a Component of the given Type.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalReadException">
+        /// Thrown when the Engine does not declare that is Reads the given Component Type.
+        /// </exception>
         protected bool HasComponent<TComponent>(Entity entity) where TComponent : struct, IComponent
         {
             var pendingRead = receiveTypes.Contains(typeof(PendingComponentMessage<TComponent>));
@@ -264,6 +338,12 @@ namespace Encompass
             }
         }
 
+        /// <summary>
+        /// Sets Component data for the specified Component Type on the specified Entity. If Component data for this Type already existed on the Entity, the component data is overwritten.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalWriteException">
+        /// Thrown when the Engine does not declare that it Writes the given Component Type.
+        /// </exception>
         protected Guid SetComponent<TComponent>(Entity entity, TComponent component) where TComponent : struct, IComponent
         {
             var priority = writePriorities.ContainsKey(typeof(TComponent)) ? writePriorities[typeof(TComponent)] : 0;
@@ -288,11 +368,22 @@ namespace Encompass
             return componentID;
         }
 
+        /// <summary>
+        /// Overwrites Component struct data associated with the specified Component ID. 
+        /// </summary>
         protected Guid SetComponent<TComponent>(Guid componentID, TComponent component) where TComponent : struct, IComponent
         {
             return SetComponent(GetEntityByComponentID<TComponent>(componentID), component);
         }
 
+        /// <summary>
+        /// Sets Draw Component data for the specified Component Type on the specified Entity. 
+        /// This method must be used for the Draw Component to be readable by an OrderedRenderer.
+        /// If Component data for this Type already existed on the Entity, the component data is overwritten.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalWriteException">
+        /// Thrown when the Engine does not declare that it Writes the given Component Type.
+        /// </exception>
         protected Guid SetDrawComponent<TComponent>(Entity entity, TComponent component, int layer = 0) where TComponent : struct, IComponent, IDrawComponent
         {
             var priority = writePriorities.ContainsKey(typeof(TComponent)) ? writePriorities[typeof(TComponent)] : 0;
@@ -317,6 +408,12 @@ namespace Encompass
             return componentID;
         }
 
+        /// <summary>
+        /// Sends a Message.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalSendException">
+        /// Thrown when the Engine does not declare that it Sends the Message Type.
+        /// </exception>
         protected void SendMessage<TMessage>(TMessage message) where TMessage : struct, IMessage
         {
             if (!sendTypes.Contains(typeof(TMessage)))
@@ -327,6 +424,10 @@ namespace Encompass
             messageManager.AddMessage(message);
         }
 
+        /// <summary>
+        /// Sends a message after the specified number of seconds.
+        /// </summary>
+        /// <param name="time">The time in seconds that will elapse before the message is sent.</param>
         protected void SendMessageDelayed<TMessage>(TMessage message, double time) where TMessage : struct, IMessage
         {
             messageManager.AddMessageDelayed(message, time);
@@ -355,6 +456,12 @@ namespace Encompass
             componentMessageManager.AddPendingComponentMessage(message);
         }
 
+        /// <summary>
+        /// Reads all messages of the specified Type.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalReadException">
+        /// Thrown when the Engine does not declare that it Receives the specified Message Type.
+        /// </exception>
         protected IEnumerable<TMessage> ReadMessages<TMessage>() where TMessage : struct, IMessage
         {
             if (!receiveTypes.Contains(typeof(TMessage)))
@@ -365,11 +472,23 @@ namespace Encompass
             return messageManager.GetMessagesByType<TMessage>();
         }
 
+        /// <summary>
+        /// Reads an arbitrary message of the specified Type.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalReadException">
+        /// Thrown when the Engine does not declare that it Receives the specified Message Type.
+        /// </exception>
         protected TMessage ReadMessage<TMessage>() where TMessage : struct, IMessage
         {
             return ReadMessages<TMessage>().First();
         }
 
+        /// <summary>
+        /// Returns true if a Message of the specified Type has been sent this frame.
+        /// </summary>
+        /// <exception cref="Encompass.Exceptions.IllegalReadException">
+        /// Thrown when the Engine does not declare that it Receives the specified Message Type.
+        /// </exception>
         protected bool SomeMessage<TMessage>() where TMessage : struct, IMessage
         {
             if (!receiveTypes.Contains(typeof(TMessage)))
@@ -380,11 +499,48 @@ namespace Encompass
             return ReadMessages<TMessage>().Any();
         }
 
+        /// <summary>
+        /// Destroys the Entity with the specified ID. This also removes all of the Components associated with the Entity.
+        /// Entity destruction takes place after all the Engines have been processed by World Update.
+        /// </summary>
         protected void Destroy(Guid entityID)
         {
             entityManager.MarkForDestroy(entityID);
         }
 
+        /// <summary>
+        /// Destroys the specified Entity. This also removes all of the Components associated with the Entity.
+        /// Entity destruction takes place after all the Engines have been processed by World Update.
+        /// </summary>
+        protected void Destroy(Entity entity)
+        {
+            entityManager.MarkForDestroy(entity.ID);
+        }
+
+        /// <summary>
+        /// Destroys an arbitrary Entity containing a Component of the specified Type.
+        /// Entity destruction takes place after all the Engines have been processed by World Update.
+        /// </summary>
+        protected void DestroyWith<TComponent>() where TComponent : struct, IComponent
+        {
+            Destroy(ReadEntity<TComponent>());
+        }
+
+        /// <summary>
+        /// Destroys all Entities containing a Component of the specified Type.
+        /// Entity destruction takes place after all the Engines have been processed by World Update.
+        /// </summary>
+        protected void DestroyAllWith<TComponent>() where TComponent : struct, IComponent
+        {
+            foreach (var entity in ReadEntities<TComponent>())
+            {
+                Destroy(entity);
+            }
+        }
+
+        /// <summary>
+        /// Removes the Component with the specified ID from its Entity.
+        /// </summary>
         protected void RemoveComponent(Guid componentID)
         {
             componentManager.MarkForRemoval(componentID);

encompass-cs/Engines/Spawner.cs

@@ -2,6 +2,10 @@
 
 namespace Encompass.Engines
 {
+    /// <summary>
+    /// A Spawner is a special type of Engine that runs a Spawn method in response to each Message it receives.
+    /// Spawners are useful for organizing the building of new Entities in your game.
+    /// </summary>
     public abstract class Spawner<TMessage> : Engine where TMessage : struct, IMessage
     {
         protected Spawner() : base()

encompass-cs/Entity.cs

@@ -2,6 +2,10 @@
 
 namespace Encompass
 {
+    /// <summary>
+    /// An Entity is a structure composed of a unique ID and a collection of Components.
+    /// An Entity may only have a single Component of any particular Type.
+    /// </summary>
     public struct Entity : IEquatable<Entity>
     {
         public readonly Guid ID;

encompass-cs/Exceptions/NoComponentOfTypeException.cs

@@ -0,0 +1,25 @@
+using System;
+using System.Runtime.Serialization;
+
+namespace Encompass.Exceptions
+{
+    [Serializable]
+    internal class NoComponentOfTypeException : Exception
+    {
+        public NoComponentOfTypeException()
+        {
+        }
+
+        public NoComponentOfTypeException(string message) : base(message)
+        {
+        }
+
+        public NoComponentOfTypeException(string message, Exception innerException) : base(message, innerException)
+        {
+        }
+
+        protected NoComponentOfTypeException(SerializationInfo info, StreamingContext context) : base(info, context)
+        {
+        }
+    }
+}

encompass-cs/IComponent.cs

@@ -1,4 +1,7 @@
 namespace Encompass
 {
+    /// <summary>
+    /// Structs that implement IComponent are considered to be Components.
+    /// </summary>
     public interface IComponent { }
 }

encompass-cs/IDrawComponent.cs

@@ -1,4 +1,7 @@
 namespace Encompass
 {
+    /// <summary>
+    /// Structs that implement IDrawComponent are considered to be DrawComponents.
+    /// </summary>
     public interface IDrawComponent { }
 }

encompass-cs/IMessage.cs

@@ -1,4 +1,7 @@
 namespace Encompass
 {
+    /// <summary>
+    /// Structs that implement IMessage are considered to be Messages.
+    /// </summary>
     public interface IMessage { }
 }

encompass-cs/Renderers/GeneralRenderer.cs

@@ -1,5 +1,9 @@
 namespace Encompass
 {
+    /// <summary>
+    /// GeneralRenderer is a Renderer which generically reads the game state in order to draw elements to the screen.
+    /// GeneralRenderers have a layer specified when they are added to the World.
+    /// </summary>
     public abstract class GeneralRenderer : Renderer
     {
         public abstract void Render();

encompass-cs/Renderers/OrderedRenderer.cs

@@ -2,6 +2,9 @@
 
 namespace Encompass
 {
+    /// <summary>
+    /// OrdereredRenderer provides a structure for the common pattern of wishing to draw a specific DrawComponent at a specific layer.
+    /// </summary>
     public abstract class OrderedRenderer<TComponent> : Renderer where TComponent : struct, IComponent, IDrawComponent
     {
         public abstract void Render(Guid drawComponentID, TComponent drawComponent);

encompass-cs/World.cs

@@ -2,6 +2,9 @@ using System.Collections.Generic;
 
 namespace Encompass
 {
+    /// <summary>
+    /// The World is a collection of Engines, Renderers, Entities, Components, and Messages that compose the simulation.
+    /// </summary>
     public class World
     {
         private readonly List<Engine> enginesInOrder;
@@ -28,10 +31,14 @@ namespace Encompass
             this.renderManager = renderManager;
         }
 
+        /// <summary>
+        /// Drives the simulation. Should be called from your game engine's update loop.
+        /// </summary>
+        /// <param name="dt">The time in seconds that has passed since the previous frame.</param>
         public void Update(double dt)
         {
             messageManager.ProcessDelayedMessages(dt);
-            
+
             foreach (var engine in enginesInOrder)
             {
                 engine.Update(dt);
@@ -45,6 +52,9 @@ namespace Encompass
             componentManager.WriteComponents();
         }
 
+        /// <summary>
+        /// Causes the Renderers to draw.
+        /// </summary>
         public void Draw()
         {
             renderManager.Draw();

encompass-cs/WorldBuilder.cs

@@ -7,6 +7,14 @@ using Encompass.Engines;
 
 namespace Encompass
 {
+    /// <summary>
+    /// WorldBuilder is used to construct a World from Engines, Renderers, and an initial state of Entities, Components, and Messages.
+    /// </summary>
+    /// <remarks>
+    /// WorldBuilder enforces certain rules about Engine structure. It is forbidden to have messages create cycles between Engines,
+    /// and no Component may be written by more than one Engine.
+    /// The WorldBuilder uses Engines and their Message read/emit information to determine a valid ordering of the Engines, which is given to the World.
+    /// </remarks>
     public class WorldBuilder
     {
         private readonly List<Engine> engines = new List<Engine>();
@@ -35,26 +43,42 @@ namespace Encompass
             renderManager = new RenderManager(componentManager, drawLayerManager);
         }
 
+        /// <summary>
+        /// Creates and returns a new empty Entity.
+        /// </summary>
         public Entity CreateEntity()
         {
             return entityManager.CreateEntity();
         }
 
+        /// <summary>
+        /// Specifies that the given Message should be sent immediately on the first World Update.
+        /// </summary>
         public void SendMessage<TMessage>(TMessage message) where TMessage : struct, IMessage
         {
             messageManager.AddMessage(message);
         }
 
+        /// <summary>
+        /// Specifies that the given Message should be sent after the specified number of seconds after the first World Update.
+        /// </summary>
         public void SendMessageDelayed<TMessage>(TMessage message, double time) where TMessage : struct, IMessage
         {
             messageManager.AddMessageDelayed(message, time);
         }
 
+        /// <summary>
+        /// Sets Component data for the specified Component Type on the specified Entity.
+        /// </summary>
         public Guid SetComponent<TComponent>(Entity entity, TComponent component, int priority = 0) where TComponent : struct, IComponent
         {
             return componentManager.MarkComponentForWrite(entity, component, priority);
         }
 
+        /// <summary>
+        /// Sets Draw Component data for the specified Component Type on the specified Entity. 
+        /// This method must be used for the Draw Component to be readable by an OrderedRenderer.
+        /// </summary>
         public Guid SetDrawComponent<TComponent>(Entity entity, TComponent component, int priority = 0, int layer = 0) where TComponent : struct, IComponent, IDrawComponent
         {
             return componentManager.MarkDrawComponentForWrite(entity, component, priority, layer);
@@ -66,6 +90,10 @@ namespace Encompass
             AddEngine((Engine)Activator.CreateInstance(typeof(ComponentMessageEmitter<>).MakeGenericType(componentType)));
         }
 
+        /// <summary>
+        /// Adds the specified Engine to the World.
+        /// </summary>
+        /// <param name="engine">An instance of an Engine.</param>
         public Engine AddEngine<TEngine>(TEngine engine) where TEngine : Engine
         {
             engine.AssignEntityManager(entityManager);
@@ -126,6 +154,9 @@ namespace Encompass
             return engine;
         }
 
+        /// <summary>
+        /// Adds the specified OrderedRenderer to the World.
+        /// </summary>
         public OrderedRenderer<TComponent> AddOrderedRenderer<TComponent>(OrderedRenderer<TComponent> renderer) where TComponent : struct, IComponent, IDrawComponent
         {
             renderer.AssignEntityManager(entityManager);
@@ -134,6 +165,12 @@ namespace Encompass
             return renderer;
         }
 
+        /// <summary>
+        /// Adds the specified GeneralRenderer to the World at the specified layer.
+        /// Higher layer numbers draw on top of lower layer numbers.
+        /// </summary>
+        /// <param name="renderer">An instance of a GeneralRenderer.</param>
+        /// <param name="layer">The layer at which the GeneralRenderer should render. Higher numbers draw over lower numbers.</param>
         public TRenderer AddGeneralRenderer<TRenderer>(TRenderer renderer, int layer) where TRenderer : GeneralRenderer
         {
             renderer.AssignEntityManager(entityManager);
@@ -164,6 +201,11 @@ namespace Encompass
             }
         }
 
+        /// <summary>
+        /// Builds the World out of the state specified on the WorldBuilder.
+        /// Validates and constructs an ordering of the given Engines.
+        /// </summary>
+        /// <returns>An instance of World.</returns>
         public World Build()
         {
             BuildEngineGraph();

test/EngineTest.cs

@@ -487,6 +487,38 @@ namespace Tests
             Assert.That(results, Does.Contain((componentCID, mockComponent)));
         }
 
+        [Receives(typeof(DestroyComponentMessage))]
+        class DestroyEntityEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                foreach (var message in ReadMessages<DestroyComponentMessage>())
+                {
+                    Destroy(message.entity);
+                }
+            }
+        }
+
+        [Test]
+        public void DestroyEntityWithoutID()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new AddComponentEngine());
+            worldBuilder.AddEngine(new DestroyEntityEngine());
+            worldBuilder.AddEngine(new ReaderEngine());
+
+            var mockComponent = new MockComponent { };
+            var entity = worldBuilder.CreateEntity();
+            var componentID = worldBuilder.SetComponent(entity, mockComponent);
+            worldBuilder.SendMessage(new DestroyComponentMessage { entity = entity });
+
+            var world = worldBuilder.Build();
+            world.Update(0.01);
+
+            Assert.DoesNotThrow(() => world.Update(0.01));
+            Assert.That(results, Does.Not.Contain((componentID, mockComponent)));
+        }
+
         [Reads(typeof(DestroyerComponent), typeof(MockComponent))]
         class DestroyAndAddComponentEngine : Engine
         {
@@ -681,7 +713,7 @@ namespace Tests
             Assert.Throws<ComponentTypeMismatchException>(() => world.Update(0.01f));
         }
 
-        struct EntityIDComponent : IComponent { public Guid entityID;  }
+        struct EntityIDComponent : IComponent { public Guid entityID; }
         static bool hasEntity;
 
         [Reads(typeof(EntityIDComponent))]
@@ -774,7 +806,7 @@ namespace Tests
                 foreach (var (componentID, component) in ReadComponents<MockComponent>())
                 {
                     RemoveComponent(componentID);
-                    SendMessageDelayed(new MockMessage {}, 1);
+                    SendMessageDelayed(new MockMessage { }, 1);
                 }
             }
         }
@@ -787,9 +819,9 @@ namespace Tests
             var worldBuilder = new WorldBuilder();
             worldBuilder.AddEngine(new DelayedMessageEngine());
             worldBuilder.AddEngine(new MessageReadEngine());
-            
+
             var entity = worldBuilder.CreateEntity();
-            worldBuilder.SetComponent(entity, new MockComponent {});
+            worldBuilder.SetComponent(entity, new MockComponent { });
 
             var world = worldBuilder.Build();
 
@@ -817,7 +849,7 @@ namespace Tests
                 foreach (var message in ReadMessages<MockMessage>())
                 {
                     var entity = CreateEntity();
-                    SetComponent(entity, new MockComponent {});
+                    SetComponent(entity, new MockComponent { });
                 }
             }
         }
@@ -841,7 +873,7 @@ namespace Tests
             worldBuilder.AddEngine(new ActivateComponentEngine());
             worldBuilder.AddEngine(new RemoveComponentEngine());
 
-            worldBuilder.SendMessage(new MockMessage {});
+            worldBuilder.SendMessage(new MockMessage { });
 
             var world = worldBuilder.Build();
 
@@ -858,13 +890,13 @@ namespace Tests
             {
                 foreach (var (componentID, component) in ReadComponents<MockComponent>())
                 {
-                    SetComponent(componentID, new MockComponent {});
+                    SetComponent(componentID, new MockComponent { });
                 }
             }
         }
 
         [Receives(typeof(DestroyComponentMessage))]
-        class DestroyEntityEngine : Engine
+        class DestroyEntityByIDEngine : Engine
         {
             public override void Update(double dt)
             {
@@ -880,16 +912,133 @@ namespace Tests
         {
             var worldBuilder = new WorldBuilder();
             worldBuilder.AddEngine(new AddComponentEngine());
-            worldBuilder.AddEngine(new DestroyEntityEngine());
+            worldBuilder.AddEngine(new DestroyEntityByIDEngine());
 
             var entity = worldBuilder.CreateEntity();
-            worldBuilder.SetComponent(entity, new MockComponent {});
+            worldBuilder.SetComponent(entity, new MockComponent { });
             worldBuilder.SendMessage(new DestroyComponentMessage { entity = entity });
 
             var world = worldBuilder.Build();
             world.Update(0.01);
-            
+
             Assert.DoesNotThrow(() => world.Update(0.01));
         }
+
+        static Entity readEntity;
+
+        [Reads(typeof(MockComponent))]
+        class ReadEntityByComponentTypeEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                readEntity = ReadEntity<MockComponent>();
+            }
+        }
+
+        [Test]
+        public void GetEntityByComponentType()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadEntityByComponentTypeEngine());
+
+            var entity = worldBuilder.CreateEntity();
+            worldBuilder.SetComponent(entity, new MockComponent { });
+
+            var world = worldBuilder.Build();
+            world.Update(0.01);
+
+            entity.Should().BeEquivalentTo(readEntity);
+        }
+
+
+
+        static Entity[] readEntities;
+
+        [Reads(typeof(MockComponent))]
+        class ReadEntitiesWithComponentTypeEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                readEntities = ReadEntities<MockComponent>().ToArray();
+            }
+        }
+
+        [Test]
+        public void ReadEntities()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadEntitiesWithComponentTypeEngine());
+            worldBuilder.AddEngine(new DestroyAllWithEngine());
+
+            var entity = worldBuilder.CreateEntity();
+            worldBuilder.SetComponent(entity, new MockComponent { });
+
+            var entityB = worldBuilder.CreateEntity();
+            worldBuilder.SetComponent(entityB, new MockComponent { });
+
+            var world = worldBuilder.Build();
+            world.Update(0.01);
+
+            readEntities.Should().Contain(entity);
+            readEntities.Should().Contain(entityB);
+        }
+
+        [Reads(typeof(MockComponent))]
+        class DestroyWithEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                if (SomeComponent<MockComponent>())
+                {
+                    DestroyWith<MockComponent>();
+                }
+            }
+        }
+
+        [Test]
+        public void DestroyWith()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadEntitiesWithComponentTypeEngine());
+            worldBuilder.AddEngine(new DestroyWithEngine());
+
+            var entity = worldBuilder.CreateEntity();
+            worldBuilder.SetComponent(entity, new MockComponent { });
+
+            var world = worldBuilder.Build();
+            world.Update(0.01);
+            world.Update(0.01); // update twice so the read happens after destroy
+
+            readEntities.Should().BeEmpty();
+        }
+
+        [Reads(typeof(MockComponent))]
+        class DestroyAllWithEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                DestroyAllWith<MockComponent>();
+            }
+        }
+
+        [Test]
+        public void DestroyAllWith()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadEntitiesWithComponentTypeEngine());
+            worldBuilder.AddEngine(new DestroyAllWithEngine());
+
+            var entity = worldBuilder.CreateEntity();
+            worldBuilder.SetComponent(entity, new MockComponent { });
+
+            var entityB = worldBuilder.CreateEntity();
+            worldBuilder.SetComponent(entityB, new MockComponent { });
+
+            var world = worldBuilder.Build();
+            world.Update(0.01);
+            world.Update(0.01); // update twice so the read happens after destroy
+
+            readEntities.Should().BeEmpty();
+        }
     }
 }

test/test.csproj

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="utf-8"?>
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFramework>netcoreapp2.1</TargetFramework>
+    <TargetFramework>netcoreapp3.0</TargetFramework>
     <IsPackable>false</IsPackable>
     <RootNamespace>Tests</RootNamespace>
     <AssemblyName>EncompassECS.Framework.Tests</AssemblyName>