Fix any_range with non-reference references can cause UB

include/boost/range/detail/any_iterator_interface.hpp

@@ -14,6 +14,7 @@
 #include <boost/iterator/iterator_categories.hpp>
 #include <boost/type_traits/add_const.hpp>
 #include <boost/type_traits/add_reference.hpp>
+#include <boost/type_traits/is_copy_constructible.hpp>
 #include <boost/type_traits/is_reference.hpp>
 #include <boost/type_traits/remove_const.hpp>
 #include <boost/type_traits/remove_reference.hpp>
@@ -35,15 +36,18 @@ namespace boost
         };
 
         template<class T>
-        struct mutable_reference_type_generator
+        struct reference_as_value_type_generator
         {
             typedef typename mpl::if_<
-                typename mpl::and_<
-                    typename is_const<T>::type,
-                    typename mpl::not_<typename is_reference<T>::type>::type
+                typename is_copy_constructible<
+                    typename remove_const<
+                        typename remove_reference<T>::type
+                    >::type
                 >::type,
-                T,
-                typename add_reference<T>::type
+                typename remove_const<
+                    typename remove_reference<T>::type
+                >::type,
+                T
             >::type type;
         };
 
@@ -53,16 +57,12 @@ namespace boost
         >
         struct any_incrementable_iterator_interface
         {
-            typedef typename mutable_reference_type_generator<
-                Reference
-            >::type reference;
-
+            typedef Reference reference;
             typedef typename const_reference_type_generator<
                 Reference
             >::type const_reference;
-
-            typedef typename remove_const<
-                typename remove_reference<Reference>::type
+            typedef typename reference_as_value_type_generator<
+                Reference
             >::type reference_as_value_type;
 
             typedef Buffer buffer_type;