encompass-cs/Collections/ComponentStore.cs

@@ -1,4 +1,5 @@
-using MoonTools.FastCollections;
+using Encompass.Exceptions;
+using MoonTools.FastCollections;
 using System;
 using System.Collections.Generic;
 
@@ -54,11 +55,15 @@ namespace Encompass
 
         public ref readonly TComponent Singular<TComponent>() where TComponent : struct
         {
+            if (!Any<TComponent>()) { throw new NoComponentOfTypeException("No component of type {0} exists", typeof(TComponent).Name); }
+
             return ref Lookup<TComponent>().Singular();
         }
 
         public ref readonly Entity SingularEntity<TComponent>() where TComponent : struct
         {
+            if (!Any<TComponent>()) { throw new NoComponentOfTypeException("No component of type {0} exists", typeof(TComponent).Name); }
+
             return ref Lookup<TComponent>().SingularEntity();
         }
 

encompass-cs/Collections/MessageStore.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using Encompass.Exceptions;
 
 namespace Encompass
 {
@@ -35,6 +36,8 @@ namespace Encompass
 
         public ref readonly TMessage First<TMessage>() where TMessage : struct, IMessage
         {
+            if (!Any<TMessage>()) { throw new NoMessageOfTypeException("No Message of type {0} exists", typeof(TMessage).Name); }
+
             return ref Lookup<TMessage>().First();
         }
 

encompass-cs/Exceptions/NoComponentOfTypeException.cs

@@ -1,25 +1,12 @@
 using System;
-using System.Runtime.Serialization;
 
 namespace Encompass.Exceptions
 {
-    [Serializable]
+    public class NoComponentOfTypeException : Exception
-    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)
     {
-        }
+        public NoComponentOfTypeException(
+            string format,
+            params object[] args
+        ) : base(string.Format(format, args)) { }
     }
 }

encompass-cs/Exceptions/NoMessageOfTypeException.cs

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

test/EngineTest.cs

@@ -17,10 +17,11 @@ namespace Tests
 
     public class EngineTest
     {
-        static MockComponent[] resultComponents;
         static MockComponent resultComponent;
+        static MockComponent[] resultComponents = new MockComponent[1];
 
-        static MockMessage[] resultMessages;
+        static MockMessage resultMessage;
+        static MockMessage[] resultMessages = new MockMessage[1];
 
         [Reads(typeof(MockComponent))]
         public class ReadComponentsTestEngine : Engine
@@ -149,6 +150,17 @@ namespace Tests
             Assert.AreEqual(mockComponent, resultComponent);
         }
 
+        [Test]
+        public void ReadComponentThrowsWhenNoneExist()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadComponentTestEngine());
+
+            var world = worldBuilder.Build();
+
+            Assert.Throws<NoComponentOfTypeException>(() => world.Update(0.01f), "No component of type MockComponent exists");
+        }
+
         [Test]
         public void ReadComponentWhenMultipleComponents()
         {
@@ -277,7 +289,7 @@ namespace Tests
         }
 
         [Receives(typeof(MockMessage))]
-        public class MessageReadEngine : Engine
+        public class ReadMessagesEngine : Engine
         {
             public override void Update(double dt)
             {
@@ -285,18 +297,38 @@ namespace Tests
             }
         }
 
+        [Receives(typeof(MockMessage))]
+        public class ReadMessageEngine : Engine
+        {
+            public override void Update(double dt)
+            {
+                resultMessage = ReadMessage<MockMessage>();
+            }
+        }
+
         [Test]
         public void EmitAndReadMessage()
         {
             var worldBuilder = new WorldBuilder();
             worldBuilder.AddEngine(new MessageEmitEngine());
-            worldBuilder.AddEngine(new MessageReadEngine());
+            worldBuilder.AddEngine(new ReadMessageEngine());
 
             var world = worldBuilder.Build();
 
             world.Update(0.01f);
 
-            Assert.AreEqual(resultMessages.First().myString, "howdy");
+            Assert.AreEqual(resultMessage.myString, "howdy");
+        }
+
+        [Test]
+        public void ReadMessageThrowsWhenNoneOfTypeExist()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadMessageEngine());
+
+            var world = worldBuilder.Build();
+
+            Assert.Throws<NoMessageOfTypeException>(() => world.Update(0.01), "No Message of type MockMessage exists");
         }
 
         public class UndeclaredMessageEmitEngine : Engine
@@ -810,7 +842,7 @@ namespace Tests
             var worldBuilder = new WorldBuilder();
             worldBuilder.AddEngine(new ActivateTimeDilationEngine());
             worldBuilder.AddEngine(new DelayedMessageEngine());
-            worldBuilder.AddEngine(new MessageReadEngine());
+            worldBuilder.AddEngine(new ReadMessagesEngine());
 
             var entity = worldBuilder.CreateEntity();
             worldBuilder.SetComponent(entity, new MockComponent { });
@@ -857,7 +889,7 @@ namespace Tests
             var worldBuilder = new WorldBuilder();
             worldBuilder.AddEngine(new ActivateTimeDilationEngine());
             worldBuilder.AddEngine(new DelayedMessageIgnoringTimeDilationEngine());
-            worldBuilder.AddEngine(new MessageReadEngine());
+            worldBuilder.AddEngine(new ReadMessagesEngine());
 
             var entity = worldBuilder.CreateEntity();
             worldBuilder.SetComponent(entity, new MockComponent { });
@@ -950,7 +982,7 @@ namespace Tests
         }
 
         [Test]
-        public void GetEntityByComponentType()
+        public void ReadEntity()
         {
             var worldBuilder = new WorldBuilder();
             worldBuilder.AddEngine(new ReadEntityByComponentTypeEngine());
@@ -964,6 +996,17 @@ namespace Tests
             entity.Should().BeEquivalentTo(readEntity);
         }
 
+        [Test]
+        public void ReadEntityThrowsWhenNoComponentOfTypeExists()
+        {
+            var worldBuilder = new WorldBuilder();
+            worldBuilder.AddEngine(new ReadEntityByComponentTypeEngine());
+
+            var world = worldBuilder.Build();
+
+            Assert.Throws<NoComponentOfTypeException>(() => world.Update(0.01), "No component of type MockComponent exists");
+        }
+
         struct MockComponentB : IComponent
         {
             private int value;