Removed warning about implicitly declared assingment operator.

Removes Warnings like this:

dune/istl/ilu.hh:49:16: warning: implicitly-declared ‘constexpr Dune::Imp::compressed_base_array_unmanaged<Dune::FieldMatrix<double, 1, 1>, long unsigned int>::RealIterator<Dune::FieldMatrix<double, 1, 1> >& Dune::Imp::compressed_base_array_unmanaged<Dune::FieldMatrix<double, 1, 1>, long unsigned int>::RealIterator<Dune::FieldMatrix<double, 1, 1> >::operator=(const Dune::Imp::compressed_base_array_unmanaged<Dune::FieldMatrix<double, 1, 1>, long unsigned int>::RealIterator<Dune::FieldMatrix<double, 1, 1> >&)’ is deprecated [-Wdeprecated-copy] 49 | for (ij=(*i).begin(); ij.index()<i.index(); ++ij) | ~~^~~~~~~~~~~~~

Some C++ expert should double check this. You cannot trust me here.

dune/istl/basearray.hh

@@ -97,17 +97,19 @@ namespace Imp {
       friend class RealIterator<ValueType>;
 
       //! constructor
-      RealIterator ()
-        : p(0), i(0)
-      {}
-
       RealIterator (const B* _p, B* _i) : p(_p), i(_i)
       {   }
 
+      RealIterator () = default;
+
       RealIterator(const RealIterator<ValueType>& it)
-        : p(it.p), i(it.i)
+      : p(it.p), i(it.i)
       {}
 
+      void operator=(const RealIterator<ValueType>& it)
+      {
+        p = it.p; i = it.i;
+      }
       //! return index
       size_type index () const
       {
@@ -163,8 +165,8 @@ namespace Imp {
         i+=d;
       }
 
-      const B* p;
-      B* i;
+        const B* p{};
+        B* i{};
     };
 
     //! iterator type for sequential access
@@ -259,17 +261,15 @@ namespace Imp {
       return p;
     }
 
+    base_array_unmanaged () = default;
   protected:
-    //! makes empty array
-    base_array_unmanaged ()
-      : n(0), p(0)
-    {}
     //! make an initialized array
     base_array_unmanaged (size_type n_, B* p_)
       : n(n_), p(p_)
     {}
-    size_type n;     // number of elements in array
-    B *p;      // pointer to dynamically allocated built-in array
+
+    size_type n{};     // number of elements in array
+    B *p{};      // pointer to dynamically allocated built-in array
   };
 
 
@@ -348,23 +348,25 @@ namespace Imp {
       friend class RealIterator<const ValueType>;
       friend class RealIterator<ValueType>;
 
-      //! constructor
-      RealIterator ()
-        : p(0), j(0), i(0)
-      {}
-
       //! constructor
       RealIterator (B* _p, size_type* _j, size_type _i)
         : p(_p), j(_j), i(_i)
       {       }
 
+      RealIterator () = default;
+
       /**
        * @brief Copy constructor from mutable iterator
        */
+        // template<typename V,typename = std::enable_if_t<!std::is_same<V,T>::value,void>>
       RealIterator(const RealIterator<ValueType>& it)
         : p(it.p), j(it.j), i(it.i)
       {}
 
+      void operator=(const RealIterator<ValueType>& it)
+      {
+        p = it.p; j = it.j; i = it.i;
+      }
 
       //! equality
       bool equals (const RealIterator<ValueType>& it) const
@@ -424,9 +426,9 @@ namespace Imp {
         return p[i];
       }
 
-      B* p;
-      size_type* j;
-      size_type i;
+      B* p{};
+      size_type* j{};
+      size_type i{};
     };
 
     /** @brief The iterator type. */