DispatchOnChange and DispatchOnSet must hold only value types

fix QueryGroupedEntityViews

Svelto.ECS/Dispatcher/DispatchOnChange.cs

@@ -2,14 +2,12 @@ using System.Collections.Generic;
 
 namespace Svelto.ECS
 {
-    public class DispatchOnChange<T> : DispatchOnSet<T>
+    public class DispatchOnChange<T> : DispatchOnSet<T> where T:struct
     {
         public DispatchOnChange(int senderID) : base(senderID)
         { }
 
-        public DispatchOnChange() 
-        {
-        }
+        public DispatchOnChange() {}
 
         public new T value
         {

Svelto.ECS/Dispatcher/DispatchOnSet.cs

@@ -2,7 +2,7 @@ using Svelto.WeakEvents;
 
 namespace Svelto.ECS
 {
-    public class DispatchOnSet<T>
+    public class DispatchOnSet<T> where T:struct
     {
         public DispatchOnSet(int senderID)
         {
@@ -42,8 +42,8 @@ namespace Svelto.ECS
         }
 
         protected T      _value;
-        protected int    _senderID;
+        readonly int    _senderID;
 
-        protected WeakEvent<int, T> _subscribers;
+        WeakEvent<int, T> _subscribers;
     }
 }

Svelto.ECS/EntityViewsDB.cs

@@ -31,12 +31,12 @@ namespace Svelto.ECS.Internal
 
         public FasterReadOnlyList<T> QueryGroupedEntityViews<T>(int @group) where T:EntityView, new()
         {
-            Dictionary<Type, ITypeSafeList> entityViews;
+            Dictionary<Type, ITypeSafeList> entitiesInGroupPerType;
 
-            if (_groupEntityViewsDB.TryGetValue(group, out entityViews) == false)
+            if (_groupEntityViewsDB.TryGetValue(group, out entitiesInGroupPerType) == false)
                 return RetrieveEmptyEntityViewList<T>();
             
-            return new FasterReadOnlyList<T>(entityViews as FasterList<T>);
+            return new FasterReadOnlyList<T>((FasterList<T>) entitiesInGroupPerType[typeof(T)]);
         }
 
         public T[] QueryEntityViewsAsArray<T>(out int count) where T : IEntityView
@@ -49,9 +49,7 @@ namespace Svelto.ECS.Internal
             if (_entityViewsDB.TryGetValue(type, out entityViews) == false)
                 return RetrieveEmptyEntityViewArray<T>();
             
-            var castedEntityViews = (FasterList<T>)entityViews;
-
-            return FasterList < T > .NoVirt.ToArrayFast(castedEntityViews, out count);
+            return FasterList<T>.NoVirt.ToArrayFast((FasterList<T>)entityViews, out count);
         }
         
         public T[] QueryGroupedEntityViewsAsArray<T>(int @group, out int count) where T : IEntityView
@@ -64,11 +62,7 @@ namespace Svelto.ECS.Internal
             if (_groupEntityViewsDB.TryGetValue(group, out entityViews) == false)
                 return RetrieveEmptyEntityViewArray<T>();
                        
-            var castedEntityViews = (FasterList<T>)entityViews[type];
-
-            count = castedEntityViews.Count;
-
-            return FasterList<T>.NoVirt.ToArrayFast(castedEntityViews, out count);
+            return FasterList<T>.NoVirt.ToArrayFast((FasterList<T>)entityViews[type], out count);
         }
 
         public ReadOnlyDictionary<int, T> QueryIndexableEntityViews<T>() where T:IEntityView