Pass const reference instead of const pointers.

dune/matrix-vector/singlenonzerocolumnmatrix.hh

@@ -25,23 +25,23 @@ class SingleNonZeroColumnMatrix
         typedef IndexedSliceIterator<const K*, const K> ConstIterator;
         typedef ConstIterator const_iterator;
 
-        RowProxy(const K* value, size_type nzCol) :
+        RowProxy(const K& value, size_type nzCol) :
             value_(value),
             nzCol_(nzCol)
         {}
 
         ConstIterator begin() const
         {
-            return ConstIterator(value_, nzCol_, 0, 1);
+            return ConstIterator(&value_, nzCol_, 0, 1);
         }
 
         ConstIterator end() const
         {
-            return ConstIterator(value_, nzCol_+1, 0, 1);
+            return ConstIterator(&value_, nzCol_+1, 0, 1);
         }
 
     protected:
-        const K* value_;
+        const K& value_;
         size_type nzCol_;
     };
 
@@ -96,7 +96,7 @@ public:
 
     const_row_reference operator[] (size_type rowIndex) const
     {
-        return const_row_reference(&(static_cast<const K&>(nonZeroColumn_[rowIndex])), columnIndex_);
+        return const_row_reference(static_cast<const K&>(nonZeroColumn_[rowIndex]), columnIndex_);
     }
 
     size_type nonZeroColumnIndex() const