Make it derived class responsibility to include <boost/functional/hash.hpp>

examples/registry.cpp

@@ -12,7 +12,6 @@
 
 #include <boost/type_index.hpp>
 #include <boost/unordered_set.hpp>
-#include <boost/functional/hash.hpp>
 //<-
 // Making `#include <cassert>` visible in docs, while actually using `BOOST_TEST`
 // instead of `assert`. This is required to verify correct behavior even if NDEBUG

examples/user_defined_typeinfo.hpp

@@ -70,7 +70,15 @@ namespace my_namespace { namespace detail {
     `my_type_index` is a user created type_index class. If in doubt during this phase, you can always
     take a look at the `<boost/type_index/ctti_type_index.hpp>` or `<boost/type_index/stl_type_index.hpp>`
     files. Documentation for `type_index_facade` could be also useful.
+*/
 
+/*`
+    Since we are not going to override `type_index_facade::hash_code()` we must additionally include
+    `<boost/functional/hash.hpp>`.
+*/
+#include <boost/functional/hash.hpp>
+
+/*`
     See implementation of `my_type_index`:
 */
 namespace my_namespace {