Refactorization:

 - smoothen docu
 - name helper struct
 - add implementation namespace

dune/matrix-vector/genericvectortools.hh

-#ifndef DUNE_MATRIX_VECTOR_GENERICVECTORTOOLS_HH
+#ifndef DUNE_MATRIX_VECTOR_GENERICVECTORTOOLS_HH
 #define DUNE_MATRIX_VECTOR_GENERICVECTORTOOLS_HH
 
 /** \file
-    \brief Various tools for working with istl vectors of arbitrary nesting depth
-*/
+ *  \brief Various tools for working with istl vectors of arbitrary nesting depth
+ */
 
+#include <iostream>
 #include <dune/common/fvector.hh>
 #include <dune/common/hybridutilities.hh>
-#include <dune/matrix-vector/algorithm.hh>
-#include <iostream>
 
+#include <dune/matrix-vector/algorithm.hh>
 
-/** \brief Various tools for working with istl vectors of arbitrary nesting depth
-*/
+//! \brief Various tools for working with istl vectors of arbitrary nesting depth
 namespace Dune {
 namespace MatrixVector {
 namespace Generic { // TODO change namespace name
 
+// forward declaration for helper struct
+namespace Impl {
 template <class Vector, typename Enable = void>
-struct Helper;
+struct ScalarSwitch;
+} // end namespace Impl
 
 //! Write vector to given stream
 template <class Vector>
 void writeBinary(std::ostream& s, const Vector& v) {
-  Helper<Vector>::writeBinary(s, v);
+  Impl::ScalarSwitch<Vector>::writeBinary(s, v);
 }
 
 //! Read vector from given stream
 template <class Vector>
 void readBinary(std::istream& s, Vector& v) {
-  Helper<Vector>::readBinary(s, v);
+  Impl::ScalarSwitch<Vector>::readBinary(s, v);
 }
 
 //! Truncate vector by given bit set
 template <class Vector, class BitVector>
 void truncate(Vector& v, const BitVector& tr) {
-  Helper<Vector>::truncate(v, tr);
+  Impl::ScalarSwitch<Vector>::truncate(v, tr);
 }
 
+namespace Impl {
+
 //! recursion helper for scalars nested in iterables (vectors)
 template <class Vector>
-struct Helper<Vector, typename std::enable_if_t<not IsNumber<Vector>::value>> {
+struct ScalarSwitch<Vector,
+                    typename std::enable_if_t<not IsNumber<Vector>::value>> {
+  using This = ScalarSwitch<Vector>;
+
   static void writeBinary(std::ostream& s, const Vector& v) {
     Hybrid::forEach(v, [&s](auto&& vi) { Generic::writeBinary(s, vi); });
   }
@@ -58,7 +65,8 @@ struct Helper<Vector, typename std::enable_if_t<not IsNumber<Vector>::value>> {
 
 //! recursion anchors for scalars
 template <class Scalar>
-struct Helper<Scalar, typename std::enable_if_t<IsNumber<Scalar>::value>> {
+struct ScalarSwitch<Scalar,
+                    typename std::enable_if_t<IsNumber<Scalar>::value>> {
   static void writeBinary(std::ostream& s, const Scalar& v) {
     s.write(reinterpret_cast<const char*>(&v), sizeof(Scalar));
   }
@@ -75,6 +83,8 @@ struct Helper<Scalar, typename std::enable_if_t<IsNumber<Scalar>::value>> {
   }
 };
 
+} // end namespace Impl
+
 } // end namespace Generic
 } // end namespace MatrixVector
 } // end namespace Dune