diff --git a/src/include/array/array_base.h b/src/include/array/array_base.h
index 0e187d6..97e48a7 100644
--- a/src/include/array/array_base.h
+++ b/src/include/array/array_base.h
@@ -45,6 +45,9 @@ namespace CNORXZ
 	/** default destructor */
 	virtual ~CArrayBase() = default;
 
+	/** Return unique pointer copy of itself. */
+	virtual Uptr<CArrayBase> copy() const = 0;
+	
 	/** const data element access.
 	    If the array's format is trivial or the index is already non-trivially formatted,
 	    this is equivalent to data()[i.pos()]. Otherwise, the array's format is applied.
diff --git a/src/include/array/marray.cc.h b/src/include/array/marray.cc.h
index d60b07d..d18391c 100644
--- a/src/include/array/marray.cc.h
+++ b/src/include/array/marray.cc.h
@@ -61,6 +61,12 @@ namespace CNORXZ
 	return *this;
     }
 
+    template <typename T>
+    Uptr<CArrayBase<T>> MArray<T>::copy() const
+    {
+	return std::make_unique<MArray<T>>(*this);
+    }
+
     template <typename T>
     const T* MArray<T>::data() const
     {
diff --git a/src/include/array/marray.h b/src/include/array/marray.h
index 384cacb..779f77b 100644
--- a/src/include/array/marray.h
+++ b/src/include/array/marray.h
@@ -38,6 +38,7 @@ namespace CNORXZ
 	MArray& init(const RangePtr& range);
 	MArray& extend(const RangePtr& range);
 
+	virtual Uptr<CArrayBase<T>> copy() const override;
 	virtual const T* data() const override;
 	virtual T* data() override;
 	virtual const_iterator cbegin() const override;
diff --git a/src/include/array/slice.cc.h b/src/include/array/slice.cc.h
index 95131b9..6d022f2 100644
--- a/src/include/array/slice.cc.h
+++ b/src/include/array/slice.cc.h
@@ -29,6 +29,12 @@ namespace CNORXZ
 	mOff(off)
     {}
 
+    template <typename T>
+    Uptr<CArrayBase<T>> CSlice<T>::copy() const
+    {
+	return std::make_unique<CSlice<T>>(*this);
+    }
+
     template <typename T>
     const T* CSlice<T>::data() const
     {
@@ -76,6 +82,12 @@ namespace CNORXZ
 	mOff(off)
     {}
 
+    template <typename T>
+    Uptr<CArrayBase<T>> Slice<T>::copy() const
+    {
+	return std::make_unique<Slice<T>>(*this);
+    }
+
     template <typename T>
     T* Slice<T>::data()
     {
diff --git a/src/include/array/slice.h b/src/include/array/slice.h
index fab06da..6acb184 100644
--- a/src/include/array/slice.h
+++ b/src/include/array/slice.h
@@ -41,7 +41,8 @@ namespace CNORXZ
 	 */
 	CSlice(const RangePtr& range, const CArrayBase<T>* parent,
 	       const YFormat& blockSizes, SizeT off);
-	
+
+	virtual Uptr<CArrayBase<T>> copy() const override;
 	virtual const T* data() const override;
 	virtual const_iterator cbegin() const override;
 	virtual const_iterator cend() const override;
@@ -82,6 +83,7 @@ namespace CNORXZ
 	Slice(const RangePtr& range, ArrayBase<T>* parent,
 	      const YFormat& blockSizes, SizeT off);
 
+	virtual Uptr<CArrayBase<T>> copy() const override;
 	virtual const T* data() const override;
 	virtual T* data() override;
 	virtual const_iterator cbegin() const override;
diff --git a/src/opt/mpi/include/rrange.h b/src/opt/mpi/include/rrange.h
index a95d192..2f636cf 100644
--- a/src/opt/mpi/include/rrange.h
+++ b/src/opt/mpi/include/rrange.h
@@ -152,13 +152,13 @@ namespace CNORXZ
 	template <class I>
 	struct is_rank_index
 	{
-	    constexpr bool value = false;
+	    static constexpr bool value = false;
 	};
 
 	template <class IndexI, class IndexK>
-	struct is_rank_index<IndexI,IndexK>
+	struct is_rank_index<RIndex<IndexI,IndexK>>
 	{
-	    constexpr bool value = true;
+	    static constexpr bool value = true;
 	};
 	
 	/** ****