Introduce MultiTypeBlockVector::N() for the number of vector entries

This is the name mandated by the dune-istl interface.

Deprecate the old name 'count'.

CHANGELOG.md

@@ -37,6 +37,9 @@
 - The interface methods `dot()` and `norm()` of ScalarProduct are now `const`. You will
   have to adjust the method signatures in your own scalar product implementations.
 
+- `MultiTypeBlockVector` now implements the interface method `N()`, which
+  returns the number of vector entries.
+
 - `MultiTypeBlockVector::count()` is now `const`
 
 - `SeqILU` can now be used with SIMD data types.
@@ -55,6 +58,9 @@
 - The method `getSolverCategory` of `OwnerOverlapCopyCommunication` is deprecated and
   will be removed after Dune 2.7. Use `category()` instead.
 
+- The method `MultiTypeBlockVector::count()` has been deprecated, because its name
+  is inconsistent with the name mandated by the `dune-istl` vector interface.
+
 # Release 2.6
 
 - `BDMatrix` objects can now be constructed and assigned from `std::initializer_list`.

dune/istl/multitypeblockvector.hh

@@ -86,10 +86,17 @@ namespace Dune {
       return sizeof...(Args);
     }
 
+    /** \brief Number of elements
+     */
+    static constexpr size_type N()
+    {
+      return sizeof...(Args);
+    }
+
     /**
      * number of elements
      */
-    int count() const
+    int count() const DUNE_DEPRECATED_MSG("Use method 'N' instead")
     {
       return sizeof...(Args);
     }

dune/istl/test/multitypeblockvectortest.cc

@@ -33,12 +33,17 @@ void testMultiVector(const MultiTypeBlockVector<Args...>& multiVector)
     std::cout << multiVector << std::endl;
 
     // test method 'count'
-    std::cout << "multi vector has " << multiVector.count() << " first level blocks" << std::endl;
+    std::cout << "multi vector has " << multiVector.N() << " first level blocks" << std::endl;
 
     static_assert(MultiTypeBlockVector<Args...>::size()==2, "Method MultiTypeBlockVector::size() returned wrong value!");
 
+DUNE_NO_DEPRECATED_BEGIN
     if (multiVector.count() != 2)
       DUNE_THROW(Exception, "Method MultiTypeBlockVector::count returned wrong value!");
+DUNE_NO_DEPRECATED_END
+
+    if (multiVector.N() != 2)
+      DUNE_THROW(Exception, "Method MultiTypeBlockVector::N returned wrong value!");
 
     // Test copy construction
     auto multiVector2 = multiVector;