[Boost-commit] svn:boost r69206 - sandbox/variadic_templates/boost/composite_storage/pack/multiple_dispatch

Subject: [Boost-commit] svn:boost r69206 - sandbox/variadic_templates/boost/composite_storage/pack/multiple_dispatch
From: cppljevans_at_[hidden]
Date: 2011-02-23 08:25:45

Author: cppljevans
Date: 2011-02-23 08:25:44 EST (Wed, 23 Feb 2011)
New Revision: 69206
URL: http://svn.boost.org/trac/boost/changeset/69206

Log:
WHAT:
  Added host_abstract metafunction to do reverse of hosts_concrete.
WHY:
  solve problem when concrete val or ref passed to functor.  In this
  case, hosts_concrete<HostConcrete>::type is undefined, resulting in
  compile-time error:

http://groups.google.com/group/comp.lang.c++/msg/824f1eac9a49d40d

WHYNOT:
  1) requires defining specialization of host_abstract for each
     derived class.
  2) causes conversion of a concrete class back to its abstract
     class and then extra virtual function calls to then
     convert back to concrete class.
-

Text files modified: 
   sandbox/variadic_templates/boost/composite_storage/pack/multiple_dispatch/reifier_visitor.hpp |    24 ++++++++++++++++++++++--                
   1 files changed, 22 insertions(+), 2 deletions(-)

Modified: sandbox/variadic_templates/boost/composite_storage/pack/multiple_dispatch/reifier_visitor.hpp
==============================================================================
--- sandbox/variadic_templates/boost/composite_storage/pack/multiple_dispatch/reifier_visitor.hpp	(original)
+++ sandbox/variadic_templates/boost/composite_storage/pack/multiple_dispatch/reifier_visitor.hpp	2011-02-23 08:25:44 EST (Wed, 23 Feb 2011)
@@ -195,6 +195,24 @@
    */
 ;
   template
+  < typename HostConcrete
+  >
+struct host_abstract
+  /**@brief
+   *  Metafunction returning Abstract class
+   *  of which HostConcrete is a member.
+   *  IOW, does inverse of hosts_concrete.
+   */
+{
+        typedef 
+      HostConcrete 
+    type
+    //By default, HostConcrete is member
+    //of a type hierarchy starting at
+    //HostConcrete.
+    ;   
+};
+  template
   < typename ReifyApply
   , typename ArgsConcreteAbstract
   >
@@ -246,8 +264,10 @@
       >
     >
   , typename hosts_concrete
-    < typename remove_cv
-      < HeadAbstract
+    < typename host_abstract
+      < typename remove_cv
+        < HeadAbstract
+        >::type
       >::type
     >::type
   >