diff --git a/src/include/map_range.h b/src/include/map_range.h
index 68307a6..6fa38c8 100644
--- a/src/include/map_range.h
+++ b/src/include/map_range.h
@@ -53,7 +53,7 @@ namespace MultiArrayTools
     class OpExpr
     {
     public:
-        typedef typename Index::OIType OIType;
+        //typedef typename Index::OIType OIType;
 	//typedef SingleIndex<typename Op::value_type,STYPE> OIType;
 	static constexpr size_t LAYER = Expr::LAYER + 1;
 	static constexpr size_t SIZE = Expr::SIZE + Op::SIZE;
diff --git a/src/include/multi_array_operation.cc.h b/src/include/multi_array_operation.cc.h
index 65ee2e9..1bb8393 100644
--- a/src/include/multi_array_operation.cc.h
+++ b/src/include/multi_array_operation.cc.h
@@ -367,6 +367,15 @@ namespace MultiArrayTools
         return mIndex.ifor(1,in.loop(AssignmentExpr<T,OpClass>(mOrigDataPtr,in)));
     }
 
+    template <typename T, class... Ranges>
+    template <class OpClass>
+    auto OperationRoot<T,Ranges...>::assignExpr(const OpClass& in) const
+        -> decltype(in.loop(AssignmentExpr<T,OpClass>(mOrigDataPtr,in)))
+    {
+        static_assert( OpClass::SIZE == decltype(in.rootSteps())::SIZE, "Ext Size mismatch" );
+        return in.loop(AssignmentExpr<T,OpClass>(mOrigDataPtr,in));
+    }
+    
     template <typename T, class... Ranges>
     template <class OpClass, class Index>
     auto OperationRoot<T,Ranges...>::assign(const OpClass& in, const std::shared_ptr<Index>& i) const
diff --git a/src/include/multi_array_operation.h b/src/include/multi_array_operation.h
index f1e08d0..ac4d6b7 100644
--- a/src/include/multi_array_operation.h
+++ b/src/include/multi_array_operation.h
@@ -315,6 +315,10 @@ namespace MultiArrayTools
         auto assign(const OpClass& in) const
             -> decltype(mIndex.ifor(1,in.loop(AssignmentExpr<T,OpClass>(mOrigDataPtr,in))));
 
+        template <class OpClass>
+        auto assignExpr(const OpClass& in) const
+            -> decltype(in.loop(AssignmentExpr<T,OpClass>(mOrigDataPtr,in)));
+        
         template <class OpClass, class Index>
         auto assign(const OpClass& in, const std::shared_ptr<Index>& i) const
             -> decltype(i->ifor(1,in.loop(AssignmentExpr2<T,OperationRoot<T,Ranges...>,OpClass>