Merge remote-tracking branch 'remotes/origin/entitystructrework' into EntityViewAsStruct

# Conflicts:
#	Svelto.ECS/DataStructures/TypeSafeFasterListForECS.cs
#	Svelto.ECS/EnginesRootEngines.cs
#	Svelto.ECS/EnginesRootEntities.cs
#	Svelto.ECS/EnginesRootSubmission.cs
#	Svelto.ECS/Extensions/Unity/GenericEntityDescriptorHolder.cs
#	Svelto.ECS/IEngine.cs
#	Svelto.ECS/IEntityDescriptorHolder.cs
#	Svelto.ECS/MultiEntityViewsEngine.cs
#	Svelto.ECS/Profiler/EngineProfiler.cs
#	Svelto.ECS/SingleEntityViewEngine.cs

Svelto.ECS/DataStructures/TypeSafeFasterListForECS.cs

@@ -14,14 +14,40 @@ namespace Svelto.ECS.Internal
         ITypeSafeList       Create();
         bool                MappedRemove(EGID entityID);
         ITypeSafeDictionary CreateIndexedDictionary();
-        IEntityData[]       ToArrayFast(out int count);
+        EGIDEnumerator      EntityIDS();
         void                AddCapacity(int capacity);
+
+        void Fill(FasterList<IHandleEntityViewEngineAbstracted> enginesForEntityView);
     }
 
-    class TypeSafeFasterListForECS<T> : FasterList<T> where T : IEntityData
+    public struct EGIDEnumerator:IEnumerable, IEnumerator
     {
-        readonly Dictionary<long, int> _mappedIndices;
+        Dictionary<long, int>.Enumerator _keysEnumerator;
+
+        public EGIDEnumerator(Dictionary<long, int> mappedIndices)
+        {
+            _keysEnumerator = mappedIndices.GetEnumerator();
+        }
+
+        public bool MoveNext()
+        {
+            return _keysEnumerator.MoveNext();
+        }
 
+        public void Reset()
+        {
+            throw new NotImplementedException();
+        }
+
+        public object Current { get { return new EGID(_keysEnumerator.Current.Key);} }
+        public IEnumerator GetEnumerator()
+        {
+            return this;
+        }
+    }
+
+    class TypeSafeFasterListForECS<T> : FasterList<T> where T : IEntityData
+    {
         protected TypeSafeFasterListForECS()
         {
             _mappedIndices = new Dictionary<long, int>();
@@ -55,7 +81,6 @@ namespace Svelto.ECS.Internal
 
             base.AddRange(entityViewListValue as FasterList<T>);
 
-
             for (var i = index; i < Count; ++i)
             {
                 try
@@ -95,10 +120,16 @@ namespace Svelto.ECS.Internal
         {
             return _mappedIndices[entityID.GID];
         }
+        
+        public EGIDEnumerator EntityIDS()
+        {
+            return new EGIDEnumerator(_mappedIndices);
+        }
+
+        readonly Dictionary<long, int> _mappedIndices;
     }
 
-    class TypeSafeFasterListForECSForStructs<T> : TypeSafeFasterListForECS<T>, ITypeSafeList
-        where T : struct, IEntityData
+    class TypeSafeFasterListForECSForStructs<T> : TypeSafeFasterListForECS<T>, ITypeSafeList where T:struct, IEntityData
     {
         public TypeSafeFasterListForECSForStructs(int size) : base(size)
         {}
@@ -118,12 +149,25 @@ namespace Svelto.ECS.Internal
 
         public ITypeSafeDictionary CreateIndexedDictionary()
         {
-            throw new NotSupportedException();
+            throw new NotImplementedException();
         }
 
-        public IEntityData[] ToArrayFast(out int count)
+        public void Fill(FasterList<IHandleEntityViewEngineAbstracted> enginesForEntityView)
         {
-            throw new Exception("Not Allowed");
+            var thisfastList = NoVirt.ToArrayFast(this);
+            for (int i = 0; i < Count; i++)
+            {
+                int count;
+                var fastList = FasterList<IHandleEntityViewEngineAbstracted>.NoVirt.ToArrayFast(enginesForEntityView, out count);
+                for (int j = 0; j < count; j++)
+                {
+#if ENGINE_PROFILER_ENABLED
+                    EngineProfiler.MonitorAddDuration<T>(fastList[j], entityView);
+#else
+                    (fastList[j] as IHandleEntityStructEngine<T>).Add(ref thisfastList[j]);
+#endif
+                }
+            }
         }
 
         public ITypeSafeList Create(int size)
@@ -131,8 +175,8 @@ namespace Svelto.ECS.Internal
             return new TypeSafeFasterListForECSForStructs<T>(size);
         }
     }
-
-    class TypeSafeFasterListForECSForClasses<T> : TypeSafeFasterListForECS<T>, ITypeSafeList where T : IEntityData, new()
+    
+    class TypeSafeFasterListForECSForClasses<T> : TypeSafeFasterListForECS<T>, ITypeSafeList where T:IEntityData, new()
     {
         public TypeSafeFasterListForECSForClasses(int size) : base(size)
         {}
@@ -155,11 +199,22 @@ namespace Svelto.ECS.Internal
             return new TypeSafeDictionaryForClass<T>();
         }
 
-        public IEntityData[] ToArrayFast(out int count)
+        public void Fill(FasterList<IHandleEntityViewEngineAbstracted> enginesForEntityView)
         {
-            count = Count;
-
-            return ToArrayFast();
+            var thisfastList = NoVirt.ToArrayFast(this);
+            for (int i = 0; i < Count; i++)
+            {
+                int count;
+                var fastList = FasterList<IHandleEntityViewEngineAbstracted>.NoVirt.ToArrayFast(enginesForEntityView, out count);
+                for (int j = 0; j < count; j++)
+                {
+#if ENGINE_PROFILER_ENABLED
+                    EngineProfiler.MonitorAddDuration(fastList[j], entityView);
+#else
+                    (fastList[j] as IHandleEntityStructEngine<T>).Add(ref thisfastList[j]);
+#endif
+                }
+            }
         }
 
         public ITypeSafeList Create(int size)

Svelto.ECS/EGID.cs

@@ -31,6 +31,11 @@ namespace Svelto.ECS
             _GID = MAKE_GLOBAL_ID(entityID, ExclusiveGroups.StandardEntity);
         }
 
+        internal EGID(long otherID)
+        {
+            _GID = otherID;
+        }
+
         static long MAKE_GLOBAL_ID(int entityId, int groupId)
         {
             return (long)groupId << 32 | (uint)entityId;

Svelto.ECS/EnginesRoot.GenericEntityFactory.cs

@@ -27,16 +27,16 @@ namespace Svelto.ECS
                 _weakEngine.Target.BuildEntity(entityID, entityDescriptor, implementors);
             }
 
-            public void BuildEntityInGroup<T>(int entityID, int groupID, object[] implementors)
+            public void BuildEntity<T>(int entityID, int groupID, object[] implementors)
                 where T : IEntityDescriptor, new()
             {
-                _weakEngine.Target.BuildEntityInGroup<T>(entityID, groupID, implementors);
+                _weakEngine.Target.BuildEntity<T>(entityID, groupID, implementors);
             }
 
-            public void BuildEntityInGroup(int entityID, int groupID, EntityDescriptorInfo entityDescriptor,
+            public void BuildEntity(int entityID, int groupID, EntityDescriptorInfo entityDescriptor,
                                            object[] implementors)
             {
-                _weakEngine.Target.BuildEntityInGroup(entityID, groupID, entityDescriptor, implementors);
+                _weakEngine.Target.BuildEntity(entityID, groupID, entityDescriptor, implementors);
             }
 
             public void PreallocateEntitySpace<T>(int size) where T : IEntityDescriptor, new()
@@ -44,7 +44,7 @@ namespace Svelto.ECS
                 _weakEngine.Target.Preallocate<T>(ExclusiveGroups.StandardEntity, size);
             }
             
-            public void PreallocateEntitySpaceInGroup<T>(int groupID, int size) where T : IEntityDescriptor, new()
+            public void PreallocateEntitySpace<T>(int groupID, int size) where T : IEntityDescriptor, new()
             {
                 _weakEngine.Target.Preallocate<T>(groupID, size);
             }

Svelto.ECS/EnginesRootEngines.cs

@@ -34,18 +34,18 @@ namespace Svelto.ECS
         /// </summary>
         public EnginesRoot(EntitySubmissionScheduler entityViewScheduler)
         {
-            _entityViewEngines = new Dictionary<Type, FasterList<IHandleEntityViewEngine>>();
+            _entityViewEngines = new Dictionary<Type, FasterList<IHandleEntityViewEngineAbstracted>>();
             _otherEngines = new FasterList<IEngine>();
 
-            _globalEntityViewsDB = new Dictionary<Type, ITypeSafeList>();
             _groupEntityViewsDB = new Dictionary<int, Dictionary<Type, ITypeSafeList>>();
+            _groupEntityViewsDB[ExclusiveGroups.StandardEntity] = new Dictionary<Type, ITypeSafeList>();
             _globalEntityViewsDBDic = new Dictionary<Type, ITypeSafeDictionary>();
             
             _entityInfos = new Dictionary<long, IEntityViewBuilder[]>();
             
             _groupedEntityViewsToAdd = new DoubleBufferedEntityViews<Dictionary<int, Dictionary<Type, ITypeSafeList>>>();
 
-            _DB = new EntityViewsDB(_globalEntityViewsDB, _globalEntityViewsDBDic, _groupEntityViewsDB);
+            _DB = new EntityViewsDB(_globalEntityViewsDBDic, _groupEntityViewsDB);
 
             _scheduler = entityViewScheduler;
             _scheduler.Schedule(new WeakAction(SubmitEntityViews));
@@ -56,7 +56,7 @@ namespace Svelto.ECS
 #if ENGINE_PROFILER_ENABLED && UNITY_EDITOR
             Profiler.EngineProfiler.AddEngine(engine);
 #endif
-            var viewEngine = engine as IHandleEntityViewEngine;
+            var viewEngine = engine as IHandleEntityViewEngineAbstracted;
             
             if (viewEngine != null)
                 CheckEntityViewsEngine(viewEngine);
@@ -75,12 +75,13 @@ namespace Svelto.ECS
         {
             var baseType = engine.GetType().GetBaseType();
 
-            while (baseType != _object)
+            while (baseType != _objectType)
             {
                 if (baseType.IsGenericTypeEx())
                 {
                     var genericArguments = baseType.GetGenericArgumentsEx();
-                    AddEngine(engine as IHandleEntityViewEngine, genericArguments, _entityViewEngines);
+                    
+                    AddEngine(engine as IHandleEntityViewEngineAbstracted, genericArguments, _entityViewEngines);
 
                     return;
                 }
@@ -117,10 +118,11 @@ namespace Svelto.ECS
             list.Add(engine);
         }
 
-        readonly Dictionary<Type, FasterList<IHandleEntityViewEngine>> _entityViewEngines;    
+        readonly Dictionary<Type, FasterList<IHandleEntityViewEngineAbstracted>> _entityViewEngines;    
         readonly FasterList<IEngine> _otherEngines;
         
         static readonly Type _entityViewType= typeof(IEntityData);
-        static readonly Type _object = typeof(object);
+        static readonly Type _objectType = typeof(object);
+        static readonly Type _valueType = typeof(ValueType);
     }
 }

Svelto.ECS/EnginesRootEntities.cs

@@ -14,10 +14,11 @@ namespace Svelto.ECS
     {
         public void Dispose()
         {
-            foreach (var entity in _globalEntityViewsDB)
-                if (entity.Value.isQueryiableEntityView)
-                    foreach (var entityView in entity.Value)
-                        RemoveEntityViewFromEngines(_entityViewEngines, entityView as IEntityData, entity.Key);
+            foreach (var groups in _groupEntityViewsDB)
+                foreach (var entity in groups.Value)
+                    if (entity.Value.isQueryiableEntityView == true)
+                        foreach (var entityView in entity.Value)
+                            RemoveEntityViewFromEngines(_entityViewEngines, entityView as IEntityData, entity.Key);
         }
 
         ///--------------------------------------------
@@ -36,13 +37,13 @@ namespace Svelto.ECS
 
         void BuildEntity<T>(int entityID, object[] implementors = null) where T : IEntityDescriptor, new()
         {
-            BuildEntityInGroup<T>
+            BuildEntity<T>
                 (entityID, ExclusiveGroups.StandardEntity, implementors);
         }
 
         void BuildEntity(int entityID, EntityDescriptorInfo entityDescriptor, object[] implementors)
         {
-            BuildEntityInGroup
+            BuildEntity
                 (entityID, ExclusiveGroups.StandardEntity, entityDescriptor, implementors);
         }
 
@@ -55,7 +56,7 @@ namespace Svelto.ECS
         /// <param name="entityID"></param>
         /// <param name="groupID"></param>
         /// <param name="implementors"></param>
-        void BuildEntityInGroup<T>(int entityID, int groupID, object[] implementors = null)
+        void BuildEntity<T>(int entityID, int groupID, object[] implementors = null)
             where T : IEntityDescriptor, new()
         {
             EntityFactory.BuildGroupedEntityViews(entityID, groupID,
@@ -65,7 +66,7 @@ namespace Svelto.ECS
                                                   implementors);
         }
 
-        void BuildEntityInGroup(int entityID, int groupID, EntityDescriptorInfo entityDescriptor,
+        void BuildEntity(int entityID, int groupID, EntityDescriptorInfo entityDescriptor,
                                 object[] implementors = null)
         {
             EntityFactory.BuildGroupedEntityViews(entityID, groupID,
@@ -95,10 +96,6 @@ namespace Svelto.ECS
 
                 //reserve space for the global pool
                 ITypeSafeList dbList;
-                if (_globalEntityViewsDB.TryGetValue(entityViewType, out dbList) == false)
-                    _globalEntityViewsDB[entityViewType] = entityViewBuilder.Preallocate(ref dbList, size);
-                else
-                    dbList.AddCapacity(size);
 
                 //reserve space for the single group
                 Dictionary<Type, ITypeSafeList> @group;
@@ -144,8 +141,6 @@ namespace Svelto.ECS
                     InternalRemoveEntityViewFromDBDicAndEngines(entityViewType, entityGID);
                     RemoveEntityViewFromDB(@group, entityViewType, entityGID);
                 }
-
-                RemoveEntityViewFromDB(@_globalEntityViewsDB, entityViewType, entityGID);
             }
 
             _entityInfos.Remove(entityGID.GID);
@@ -163,21 +158,14 @@ namespace Svelto.ECS
         {
             foreach (var group in _groupEntityViewsDB[groupID])
             {
-                {
-                    var entityViewType = group.Key;
+                var entityViewType = group.Key;
 
-                    int count;
-                    var entities = group.Value.ToArrayFast(out count);
+                var entities = group.Value.EntityIDS();
 
-                    for (var i = 0; i < count; i++)
-                    {
-                        var entityID = entities[i].ID;
-
-                        RemoveEntityViewFromDB(@_globalEntityViewsDB, entityViewType, entityID);
-
-                        if (group.Value.isQueryiableEntityView)
-                            InternalRemoveEntityViewFromDBDicAndEngines(entityViewType, entityID);
-                    }
+                foreach (EGID entityID in entities)
+                {
+                    if (group.Value.isQueryiableEntityView)
+                        InternalRemoveEntityViewFromDBDicAndEngines(entityViewType, entityID);
                 }
             }
 
@@ -206,23 +194,23 @@ namespace Svelto.ECS
             typeSafeDictionary.Remove(id);
         }
         
-        static void RemoveEntityViewFromEngines(Dictionary<Type, FasterList<IHandleEntityViewEngine>> entityViewEngines,
-                                                IEntityData                                           entityView,
-                                                Type                                                  entityViewType)
+        static void RemoveEntityViewFromEngines(Dictionary<Type, FasterList<IHandleEntityViewEngineAbstracted>> entityViewEngines,
+                                                IEntityData entityView, Type entityViewType)
         {
-            FasterList<IHandleEntityViewEngine> enginesForEntityView;
+            FasterList<IHandleEntityViewEngineAbstracted> enginesForEntityView;
 
             if (entityViewEngines.TryGetValue(entityViewType, out enginesForEntityView))
             {
                 int count;
-                var fastList = FasterList<IHandleEntityViewEngine>.NoVirt.ToArrayFast(enginesForEntityView, out count);
+                var fastList = FasterList<IHandleEntityViewEngineAbstracted>.NoVirt.ToArrayFast(enginesForEntityView, out count);
 
                 for (var j = 0; j < count; j++)
                 {
 #if ENGINE_PROFILER_ENABLED && UNITY_EDITOR
                     EngineProfiler.MonitorRemoveDuration(fastList[j], entityView);
 #else
-                    fastList[j].Remove(entityView);
+                    var handleMixedEntityViewEngine = (fastList[j] as IHandleEntityViewEngine);
+                    handleMixedEntityViewEngine.Remove(entityView);
 #endif
                 }
             }
@@ -276,9 +264,6 @@ namespace Svelto.ECS
         
         //TODO: Use faster dictionary and merge these two?
         
-        //Global pool of entity views when engines want to manage entityViews regardless
-        //the group
-        readonly Dictionary<Type, ITypeSafeList>        _globalEntityViewsDB;
         //indexable entity views when the entity ID is known. Usually useful to handle
         //event based logic.
         readonly Dictionary<Type, ITypeSafeDictionary>  _globalEntityViewsDBDic;

Svelto.ECS/EnginesRootSubmission.cs

@@ -57,8 +57,6 @@ namespace Svelto.ECS
                     //add the entity View in the group
                     if (entityViewsPerType.Value.isQueryiableEntityView == true)
                         AddEntityViewToDB(groupDB, entityViewsPerType);
-                    //add the entity view in the gloal pool
-                    AddEntityViewToDB(_globalEntityViewsDB, entityViewsPerType);
                     //and it's not a struct, add in the indexable DB too
                     AddEntityViewToEntityViewsDictionary(_globalEntityViewsDBDic, entityViewsPerType.Value, entityViewsPerType.Key);
                 }
@@ -66,16 +64,16 @@ namespace Svelto.ECS
 
             //then submit everything in the engines, so that the DB is up to date
             //with all the entity views and struct created by the entity built
-            foreach (var group in groupsToSubmit)
+            foreach (var groupToSubmit in groupsToSubmit)
             {
-                foreach (var entityViewList in group.Value)
+                foreach (var entityViewsPerType in groupToSubmit.Value)
                 {
-                    if (entityViewList.Value.isQueryiableEntityView)
-                    {
-                        var type = entityViewList.Key;
-                        for (var current = type; current != _entityViewType; current = current.BaseType)
-                            AddEntityViewToTheSuitableEngines(_entityViewEngines, entityViewList.Value, current);
-                    }
+                    var type = entityViewsPerType.Key;
+                    for (var current = type;
+                         current != _entityViewType && current != _objectType && current != _valueType;
+                         current = current.BaseType)
+                        AddEntityViewToTheSuitableEngines(_entityViewEngines, entityViewsPerType.Value,
+                                                          current);
                 }
             }
         }
@@ -108,30 +106,15 @@ namespace Svelto.ECS
             }
         }
 
-        static void AddEntityViewToTheSuitableEngines(Dictionary<Type, FasterList<IHandleEntityViewEngine>> entityViewEngines, ITypeSafeList entityViewsList, Type entityViewType)
+        static void AddEntityViewToTheSuitableEngines(Dictionary<Type, FasterList<IHandleEntityViewEngineAbstracted>> entityViewEngines, 
+        ITypeSafeList entityViewsList, 
+        Type entityViewType)
         {
-            FasterList<IHandleEntityViewEngine> enginesForEntityView;
+            FasterList<IHandleEntityViewEngineAbstracted> enginesForEntityView;
 
             if (entityViewEngines.TryGetValue(entityViewType, out enginesForEntityView))
             {
-                int viewsCount;
-
-                var entityViews = entityViewsList.ToArrayFast(out viewsCount);
-
-                for (int i = 0; i < viewsCount; i++)
-                {
-                    int count;
-                    var fastList = FasterList<IHandleEntityViewEngine>.NoVirt.ToArrayFast(enginesForEntityView, out count);
-                    IEntityData entityView = entityViews[i];
-                    for (int j = 0; j < count; j++)
-                    {
-#if ENGINE_PROFILER_ENABLED && UNITY_EDITOR
-                        EngineProfiler.MonitorAddDuration(fastList[j], entityView);
-#else
-                        fastList[j].Add(entityView);
-#endif
-                    }
-                }
+                entityViewsList.Fill(enginesForEntityView);
             }
         }
         

Svelto.ECS/EntityFactory.cs

@@ -1,8 +1,5 @@
 using System;
 using System.Collections.Generic;
-using Svelto.DataStructures;
-using Svelto.Utilities;
-using Console = Utility.Console;
 
 namespace Svelto.ECS.Internal
 {
@@ -59,8 +56,6 @@ namespace Svelto.ECS.Internal
             var entityViewsPoolWillBeCreated =
                 entityViewsByType.TryGetValue(entityViewType, out entityViewsList) == false;
 
-            IEntityData entityViewObjectToFill;
-
             //passing the undefined entityViewsByType inside the entityViewBuilder will allow
             //it to be created with the correct type and casted back to the undefined list.
             //that's how the list will be eventually of the target type.

Svelto.ECS/EntityViewBuilder.cs

@@ -6,7 +6,7 @@ using Svelto.Utilities;
 
 namespace Svelto.ECS
 {
-    public class EntityViewBuilder<EntityViewType> : IEntityViewBuilder where EntityViewType : IEntityData
+    public class EntityViewBuilder<EntityViewType> : IEntityViewBuilder where EntityViewType : IEntityData, new()
     {
         public void BuildEntityViewAndAddToList(ref ITypeSafeList list, EGID entityID, object[] implementors)
         {

Svelto.ECS/EntityViewsDB.cs

@@ -6,11 +6,9 @@ namespace Svelto.ECS.Internal
 {
     class EntityViewsDB : IEntityViewsDB
     {
-        internal EntityViewsDB(  Dictionary<Type, ITypeSafeList> entityViewsDB,
-                                Dictionary<Type, ITypeSafeDictionary> entityViewsDBdic,
+        internal EntityViewsDB(  Dictionary<Type, ITypeSafeDictionary> entityViewsDBdic,
                                 Dictionary<int, Dictionary<Type, ITypeSafeList>>  groupEntityViewsDB)
         {
-            _globalEntityViewsDB = entityViewsDB;
             _groupedEntityViewsDBDic = entityViewsDBdic;
             _groupEntityViewsDB = groupEntityViewsDB;
         }
@@ -21,7 +19,7 @@ namespace Svelto.ECS.Internal
 
             ITypeSafeList entityViews;
 
-            if (_globalEntityViewsDB.TryGetValue(type, out entityViews) == false)
+            if (_groupEntityViewsDB[ExclusiveGroups.StandardEntity].TryGetValue(type, out entityViews) == false)
                 return RetrieveEmptyEntityViewList<T>();
 
             return new FasterReadOnlyList<T>((FasterList<T>)entityViews);
@@ -48,7 +46,7 @@ namespace Svelto.ECS.Internal
             
             ITypeSafeList entityViews;
 
-            if (_globalEntityViewsDB.TryGetValue(type, out entityViews) == false)
+            if (_groupEntityViewsDB[ExclusiveGroups.StandardEntity].TryGetValue(type, out entityViews) == false)
                 return RetrieveEmptyEntityViewArray<T>();
             
             return FasterList<T>.NoVirt.ToArrayFast((FasterList<T>)entityViews, out count);
@@ -122,9 +120,6 @@ namespace Svelto.ECS.Internal
      
         //grouped set of entity views, this is the standard way to handle entity views
         readonly Dictionary<int, Dictionary<Type, ITypeSafeList>> _groupEntityViewsDB;
-        //Global pool of entity views when engines want to manage entityViews regardless
-        //the group
-        readonly Dictionary<Type, ITypeSafeList> _globalEntityViewsDB;
         //indexable entity views when the entity ID is known. Usually useful to handle
         //event based logic.
         readonly Dictionary<Type, ITypeSafeDictionary> _groupedEntityViewsDBDic;

Svelto.ECS/Extensions/Unity/UnitySumbmissionEntityViewScheduler .cs

@@ -44,10 +44,10 @@ namespace Svelto.ECS.Schedulers.Unity
 
             internal WeakAction OnTick;
 
-            WaitForEndOfFrame _wait = new WaitForEndOfFrame();
+            readonly WaitForEndOfFrame _wait = new WaitForEndOfFrame();
         }
 
-        Scheduler _scheduler;
+        readonly Scheduler _scheduler;
     }
 }
 #endif

Svelto.ECS/GenericEntityDescriptor.cs

@@ -1,6 +1,6 @@
 namespace Svelto.ECS
 {
-    public abstract class GenericEntityDescriptor<T>:IEntityDescriptor where T : struct, IEntityData
+    public abstract class GenericEntityDescriptor<T>:IEntityDescriptor where T : IEntityData, new()
     {
         static GenericEntityDescriptor()
         {
@@ -16,8 +16,8 @@
         
     }
 
-    public abstract class GenericEntityDescriptor<T, U> : IEntityDescriptor     where T : struct, IEntityData 
-                                                                       where U : struct, IEntityData
+    public abstract class GenericEntityDescriptor<T, U> : IEntityDescriptor     where T : IEntityData, new() 
+                                                                       where U : IEntityData, new()
     {
         static GenericEntityDescriptor()
         {
@@ -32,9 +32,9 @@
         static readonly IEntityViewBuilder[] entityViewBuilders;
     }
 
-    public abstract class GenericEntityDescriptor<T, U, V> : IEntityDescriptor     where T : struct, IEntityData
-                                                                          where U : struct, IEntityData
-                                                                          where V : struct, IEntityData
+    public abstract class GenericEntityDescriptor<T, U, V> : IEntityDescriptor     where T : IEntityData, new()
+                                                                          where U : IEntityData, new()
+                                                                          where V : IEntityData, new()
     {
         static GenericEntityDescriptor()
         {
@@ -49,10 +49,10 @@
         static readonly IEntityViewBuilder[] entityViewBuilders;
     }
 
-    public abstract class GenericEntityDescriptor<T, U, V, W> : IEntityDescriptor     where T : struct, IEntityData
-                                                                             where U : struct, IEntityData
-                                                                             where V : struct, IEntityData
-                                                                             where W : struct, IEntityData
+    public abstract class GenericEntityDescriptor<T, U, V, W> : IEntityDescriptor     where T : IEntityData, new()
+                                                                             where U : IEntityData, new()
+                                                                             where V : IEntityData, new()
+                                                                             where W : IEntityData, new()
     {
         static GenericEntityDescriptor()
         {
@@ -67,11 +67,11 @@
         static readonly IEntityViewBuilder[] entityViewBuilders;
     }
 
-    public abstract class GenericEntityDescriptor<T, U, V, W, X> : IEntityDescriptor     where T : struct, IEntityData
-                                                                                where U : struct, IEntityData
-                                                                                where V : struct, IEntityData
-                                                                                where W : struct, IEntityData
-                                                                                where X : struct, IEntityData
+    public abstract class GenericEntityDescriptor<T, U, V, W, X> : IEntityDescriptor     where T : IEntityData, new()
+                                                                                where U : IEntityData, new()
+                                                                                where V : IEntityData, new()
+                                                                                where W : IEntityData, new()
+                                                                                where X : IEntityData, new()
     {
         static GenericEntityDescriptor()
         {
@@ -86,12 +86,12 @@
         static readonly IEntityViewBuilder[] entityViewBuilders;
     }
 
-    public abstract class GenericEntityDescriptor<T, U, V, W, X, Y> : IEntityDescriptor     where T : struct, IEntityData
-                                                                                   where U : struct, IEntityData
-                                                                                   where V : struct, IEntityData
-                                                                                   where W : struct, IEntityData
-                                                                                   where X : struct, IEntityData
-                                                                                   where Y : struct, IEntityData
+    public abstract class GenericEntityDescriptor<T, U, V, W, X, Y> : IEntityDescriptor     where T : IEntityData, new()
+                                                                                   where U : IEntityData, new()
+                                                                                   where V : IEntityData, new()
+                                                                                   where W : IEntityData, new()
+                                                                                   where X : IEntityData, new()
+                                                                                   where Y : IEntityData, new()
     {
         static GenericEntityDescriptor()
         {

Svelto.ECS/IEngine.cs

@@ -1,8 +1,12 @@
+using Svelto.ECS.Internal;
+
 namespace Svelto.ECS.Internal
 {
-    public interface IHandleEntityViewEngine : IEngine
+    public interface IHandleEntityViewEngineAbstracted : IEngine
+    {}
+    
+    public interface IHandleEntityViewEngine : IHandleEntityViewEngineAbstracted
     {
-        void Add(IEntityData    entityView);
         void Remove(IEntityData entityView);
     }
 }
@@ -10,6 +14,10 @@ namespace Svelto.ECS.Internal
 namespace Svelto.ECS
 {
     public interface IEngine
+    {}
+    
+    public interface IHandleEntityStructEngine<T> : IHandleEntityViewEngineAbstracted
     {
+        void Add(ref T entityView);
     }
 }

Svelto.ECS/IEntityFactory.cs

@@ -17,7 +17,7 @@ namespace Svelto.ECS
         /// <typeparam name="T"></typeparam>
         /// <param name="size"></param>
         void PreallocateEntitySpace<T>(int size) where T : IEntityDescriptor, new();
-        void PreallocateEntitySpaceInGroup<T>(int groupID, int size) where T : IEntityDescriptor, new();
+        void PreallocateEntitySpace<T>(int groupID, int size) where T : IEntityDescriptor, new();
 
         /// <summary>
         ///     Using this function is like building a normal entity, but the entityViews
@@ -29,8 +29,8 @@ namespace Svelto.ECS
         /// <param name="groupID"></param>
         /// <param name="ed"></param>
         /// <param name="implementors"></param>
-        void BuildEntityInGroup<T>(int entityID, int groupID, object[] implementors) where T:IEntityDescriptor, new();
-        void BuildEntityInGroup(int entityID, int groupID, EntityDescriptorInfo entityDescriptor, object[] implementors);
+        void BuildEntity<T>(int entityID, int groupID, object[] implementors) where T:IEntityDescriptor, new();
+        void BuildEntity(int entityID, int groupID, EntityDescriptorInfo entityDescriptor, object[] implementors);
 
         /// <summary>
         ///     The EntityDescriptor doesn't need to be ever instantiated. It just describes the Entity

Svelto.ECS/IEntityView.cs

@@ -7,12 +7,22 @@ using Svelto.Utilities;
 namespace Svelto.ECS
 {   
     //todo: can I remove the ID from the struct?
-    
     public interface IEntityData
     {
         EGID ID { get; set; }
     }
     
+    public class EntityView : IEntityData
+    {
+        public EGID ID
+        {
+            get { return _ID; }
+            set { _ID = value; }
+        }
+
+        EGID _ID;
+    }
+    
     static class EntityView<T> where T: IEntityData, new()
     {
         internal static T BuildEntityView(EGID ID) 

Svelto.ECS/MultiEntityViewsEngine.cs

@@ -2,11 +2,12 @@ using Svelto.ECS.Internal;
 
 namespace Svelto.ECS.Internal
 {
-    public abstract class MultiEntityViewsEngine<T> : IHandleEntityViewEngine where T : class, IEntityData
+    public abstract class MultiEntityViewsEngine<T>:IHandleEntityStructEngine<T>, 
+                                                    IHandleEntityViewEngine where T:IEntityData
     {
-        public virtual void Add(IEntityData entityView)
+        public void Add(ref T entityView)
         {
-            Add((T) entityView);
+            Add(entityView);
         }
 
         public virtual void Remove(IEntityData entityView)
@@ -14,27 +15,19 @@ namespace Svelto.ECS.Internal
             Remove((T) entityView);
         }
 
-        protected abstract void Add(T    entityView);
+        protected abstract void Add(T entityView);
         protected abstract void Remove(T entityView);
     }
 }
 
 namespace Svelto.ECS
 {
-    public abstract class MultiEntityViewsEngine<T, U> : MultiEntityViewsEngine<T>
-        where U : class, IEntityData where T : class, IEntityData
+    public abstract class MultiEntityViewsEngine<T, U> : MultiEntityViewsEngine<T>, IHandleEntityStructEngine<U>
+        where U : IEntityData where T : IEntityData
     {
         protected abstract void Add(U    entityView);
         protected abstract void Remove(U entityView);
 
-        public override void Add(IEntityData entityView)
-        {
-            if (entityView is U)
-                Add((U) entityView);
-            else
-                base.Add(entityView);
-        }
-
         public override void Remove(IEntityData entityView)
         {
             if (entityView is U)
@@ -42,22 +35,19 @@ namespace Svelto.ECS
             else
                 base.Remove(entityView);
         }
+
+        public void Add(ref U entityView)
+        {
+            Add(entityView);
+        }
     }
 
-    public abstract class MultiEntityViewsEngine<T, U, V> : MultiEntityViewsEngine<T, U>
-        where V :  class, IEntityData where U :  class, IEntityData where T :  class, IEntityData
+    public abstract class MultiEntityViewsEngine<T, U, V> : MultiEntityViewsEngine<T, U>, IHandleEntityStructEngine<V>
+        where V :  IEntityData where U :  IEntityData where T :  IEntityData
     {
         protected abstract void Add(V    entityView);
         protected abstract void Remove(V entityView);
 
-        public override void Add(IEntityData entityView)
-        {
-            if (entityView is V)
-                Add((V) entityView);
-            else
-                base.Add(entityView);
-        }
-
         public override void Remove(IEntityData entityView)
         {
             if (entityView is V)
@@ -65,6 +55,11 @@ namespace Svelto.ECS
             else
                 base.Remove(entityView);
         }
+
+        public void Add(ref V entityView)
+        {
+            Add(entityView);
+        }
     }
 
     /// <summary>
@@ -72,20 +67,12 @@ namespace Svelto.ECS
     ///     if you use more than 4 nodes, your engine has
     ///     already too many responsabilities.
     /// </summary>
-    public abstract class MultiEntityViewsEngine<T, U, V, W> : MultiEntityViewsEngine<T, U, V>
-        where W :  class, IEntityData where V :  class, IEntityData where U :  class, IEntityData where T : class, IEntityData
+    public abstract class MultiEntityViewsEngine<T, U, V, W> : MultiEntityViewsEngine<T, U, V>, IHandleEntityStructEngine<W>
+        where W :  IEntityData where V :  IEntityData where U :  IEntityData where T : IEntityData
     {
         protected abstract void Add(W    entityView);
         protected abstract void Remove(W entityView);
 
-        public override void Add(IEntityData entityView)
-        {
-            if (entityView is W)
-                Add((W) entityView);
-            else
-                base.Add(entityView);
-        }
-
         public override void Remove(IEntityData entityView)
         {
             if (entityView is W)
@@ -93,5 +80,10 @@ namespace Svelto.ECS
             else
                 base.Remove(entityView);
         }
+
+        public void Add(ref W entityView)
+        {
+            Add(entityView);
+        }
     }
 }

Svelto.ECS/Profiler/EngineProfiler.cs

@@ -12,28 +12,26 @@ namespace Svelto.ECS.Profiler
     {
         static readonly Stopwatch _stopwatch = new Stopwatch();
 
-        public static readonly Dictionary<Type, EngineInfo> engineInfos = new Dictionary<Type, EngineInfo>();
-
-        public static void MonitorAddDuration(IHandleEntityViewEngine engine, IEntityData entityView)
+        public static void MonitorAddDuration<T>(IHandleEntityViewEngineAbstracted engine, T entityView)
         {
             EngineInfo info;
             if (engineInfos.TryGetValue(engine.GetType(), out info))
             {
                 _stopwatch.Start();
-                engine.Add(entityView);
+                (engine as IHandleEntityStructEngine<T>).Add(ref entityView);
                 _stopwatch.Stop();
                 info.AddAddDuration(_stopwatch.Elapsed.TotalMilliseconds);
                 _stopwatch.Reset();
             }
         }
 
-        public static void MonitorRemoveDuration(IHandleEntityViewEngine engine, IEntityData entityView)
+        public static void MonitorRemoveDuration<T>(IHandleEntityViewEngineAbstracted engine, IEntityData entityView)
         {
             EngineInfo info;
             if (engineInfos.TryGetValue(engine.GetType(), out info))
             {
                 _stopwatch.Start();
-                engine.Remove(entityView);
+                (engine as IHandleEntityViewEngine).Remove(entityView);
                 _stopwatch.Stop();
 
                 info.AddRemoveDuration(_stopwatch.Elapsed.TotalMilliseconds);
@@ -44,12 +42,19 @@ namespace Svelto.ECS.Profiler
         public static void AddEngine(IEngine engine)
         {
             if (engineInfos.ContainsKey(engine.GetType()) == false)
+            {
                 engineInfos.Add(engine.GetType(), new EngineInfo(engine));
+            }
         }
 
         public static void ResetDurations()
         {
-            foreach (var engine in engineInfos) engine.Value.ResetDurations();
+            foreach (var engine in engineInfos)
+            {
+                engine.Value.ResetDurations();
+            }
         }
+
+        public static readonly Dictionary<Type, EngineInfo> engineInfos = new Dictionary<Type, EngineInfo>();
     }
-}
+}

Svelto.ECS/SingleEntityViewEngine.cs

@@ -6,7 +6,7 @@ namespace Svelto.ECS
     {
         public void Add(IEntityData entityView)
         {
-            Add((T) entityView); //when byref returns will be vailable, this should be passed by reference, not copy!
+            Add((T) entityView);
         }
 
         public void Remove(IEntityData entityView)