[fix] use allocator traits to support containes with and without allocators

dune/istl/allocator.hh

+#ifndef DUNE_ISTL_ALLOCATOR_HH
+#define DUNE_ISTL_ALLOCATOR_HH
+
+#include <dune/common/typetraits.hh>
+#include <memory>
+
+namespace Dune {
+
+    template<typename T>
+    struct exists{
+        static const bool value = true;
+    };
+
+    template<typename T, typename = void>
+    struct DefaultAllocatorTraits
+    {
+        using type = std::allocator<T>;
+    };
+
+    template<typename T>
+    struct DefaultAllocatorTraits<T, void_t<typename T::allocator_type> >
+    {
+        using type = typename T::allocator_type;
+    };
+
+    template<typename T>
+    struct AllocatorTraits : public DefaultAllocatorTraits<T> {};
+
+    template<typename T>
+    using AllocatorType = typename AllocatorTraits<T>::type;
+
+    template<typename T, typename X>
+    using ReboundAllocatorType = typename AllocatorTraits<T>::type::template rebind<X>::other;
+
+} // end namespace Dune
+
+#endif // DUNE_ISTL_ALLOCATOR_HH

dune/istl/solvers.hh

@@ -14,6 +14,7 @@
 #include <array>
 #include <type_traits>
 
+#include "allocator.hh"
 #include "istlexception.hh"
 #include "operators.hh"
 #include "scalarproducts.hh"
@@ -907,11 +908,9 @@ namespace Dune {
     using typename IterativeSolver<X,X>::scalar_real_type;
 
     //! \bief field_type Allocator retrieved from domain type
-    using fAlloc =
-      typename X::allocator_type::template rebind<field_type>::other;
+    using fAlloc = ReboundAllocatorType<X,field_type>;
     //! \bief real_type Allocator retrieved from domain type
-    using rAlloc =
-      typename X::allocator_type::template rebind<real_type>::other;
+    using rAlloc = ReboundAllocatorType<X,real_type>;
 
   public:
 
@@ -1235,7 +1234,8 @@ namespace Dune {
     using typename IterativeSolver<X,X>::scalar_real_type;
 
     //! \bief field_type Allocator retrieved from domain type
-    typedef typename X::allocator_type::template rebind<field_type>::other fAlloc;
+    using fAlloc = ReboundAllocatorType<X,field_type>;
+
   public:
 
     /*!