Merge branch 'feature/multitype-operator' into 'releases/2.4'

Backport operator[] for MultiTypeBlockVector and MultiTypeBlockMatrix

This time for real:  This patch backports

0196c61d

and

a8f68be4

and properly adjusts them to the boost::fusion-based implementation of
MultiTypeBlockVector and MultiTypeBlockMatrix.

See merge request !25

dune/istl/multitypeblockmatrix.hh

@@ -225,6 +225,44 @@ namespace Dune {
 
     typedef typename mpl::at_c<T1,0>::type field_type;
 
+    /** \brief Random-access operator
+     *
+     * This method mimicks the behavior of normal vector access with square brackets like, e.g., m[5] = ....
+     * The problem is that the return type is different for each value of the argument in the brackets.
+     * Therefore we implement a trick using std::integral_constant.  To access the first row of
+     * a MultiTypeBlockMatrix named m write
+     * \code
+     *  std::integral_constant<std::size_t,0> _0;
+     *  m[_0] = ...
+     * \endcode
+     * The name '_0' used here as a static replacement of the integer number zero is arbitrary.
+     * Any other variable name can be used.  If you don't like the separate variable, you can writee
+     * \code
+     *  m[std::integral_constant<std::size_t,0>()] = ...
+     * \endcode
+     */
+    template< std::size_t index >
+    auto
+    operator[] ( const std::integral_constant< std::size_t, index > indexVariable ) -> decltype(fusion::at_c<index>(*this))
+    {
+      DUNE_UNUSED_PARAMETER(indexVariable);
+      return fusion::at_c<index>(*this);
+    }
+
+   /** \brief Const random-access operator
+     *
+     * This is the const version of the random-access operator.  See the non-const version for a full
+     * explanation of how to use it.
+     */
+    template< std::size_t index >
+    auto
+    operator[] ( const std::integral_constant< std::size_t, index > indexVariable ) const -> decltype(fusion::at_c<index>(*this))
+    {
+      DUNE_UNUSED_PARAMETER(indexVariable);
+      return fusion::at_c<index>(*this);
+    }
+
+
     /**
      * assignment operator
      */

dune/istl/multitypeblockvector.hh

@@ -261,6 +261,47 @@ namespace Dune {
      */
     int count() {return mpl::size<type>::value;}
 
+    /** \brief Random-access operator
+     *
+     * This method mimicks the behavior of normal vector access with square brackets like, e.g., v[5] = 1.
+     * The problem is that the return type is different for each value of the argument in the brackets.
+     * Therefore we implement a trick using std::integral_constant.  To access the first entry of
+     * a MultiTypeBlockVector named v write
+     * \code
+     *  MultiTypeBlockVector<A,B,C,D> v;
+     *  std::integral_constant<std::size_t,0> _0;
+     *  v[_0] = ...
+     * \endcode
+     * The name '_0' used here as a static replacement of the integer number zero is arbitrary.
+     * Any other variable name can be used.  If you don't like the separate variable, you can write
+     * \code
+     *  MultiTypeBlockVector<A,B,C,D> v;
+     *  v[std::integral_constant<std::size_t,0>()] = ...
+     * \endcode
+     */
+    template< std::size_t index >
+    auto
+    operator[] ( const std::integral_constant< std::size_t, index > indexVariable )
+    -> decltype(fusion::at_c<index>(*this))
+    {
+      DUNE_UNUSED_PARAMETER(indexVariable);
+      return fusion::at_c<index>(*this);
+    }
+
+    /** \brief Const random-access operator
+     *
+     * This is the const version of the random-access operator.  See the non-const version for a full
+     * explanation of how to use it.
+     */
+    template< std::size_t index >
+    auto
+    operator[] ( const std::integral_constant< std::size_t, index > indexVariable ) const
+    -> decltype(fusion::at_c<index>(*this))
+    {
+      DUNE_UNUSED_PARAMETER(indexVariable);
+      return fusion::at_c<index>(*this);
+    }
+
     /**
      * assignment operator
      */