Ticket #1860: zip_iterator.diff

.hpp

@@ -349 +349 @@
     {
     };
 
+    template<typename Iterator>
+    struct iterator_value_type
+    {
+        typedef typename iterator_traits<Iterator>::value_type type;
+    };
+
+#ifdef BOOST_MPL_CFG_NO_FULL_LAMBDA_SUPPORT
+    // Hack because BOOST_MPL_AUX_LAMBDA_SUPPORT doesn't seem to work
+    // out well.  Instantiating the nested apply template also
+    // requires instantiating iterator_traits on the
+    // placeholder. Instead we just specialize it as a metafunction
+    // class.
+    template<>
+    struct iterator_value_type<mpl::_1>
+    {
+        template <class T>
+        struct apply : iterator_value_type<T> {};
+    };
+#endif
+    
+    // Metafunction to obtain the type of the tuple whose element types
+    // are the reference types of an iterator tuple.
+    //
+    template<typename IteratorTuple>
+    struct tuple_of_value_types
+      : tuple_impl_specific::tuple_meta_transform<
+            IteratorTuple, 
+            iterator_value_type<mpl::_1>
+          >
+    {
+    };
+
     // Metafunction to obtain the minimal traversal tag in a tuple
     // of iterators.
     //
@@ -414 +446 @@
         typedef typename 
         detail::tuple_of_references<IteratorTuple>::type reference;
       
-        // Value type is the same as reference type.
-        typedef reference value_type;
+        // Value type is a tuple of the iterators' value_types
+        typedef typename
+        detail::tuple_of_value_types<IteratorTuple>::type value_type;
       
         // Difference type is the first iterator's difference type
         typedef typename iterator_traits<