From 42bff20795982459d951592bfac6196ab819d88b Mon Sep 17 00:00:00 2001
From: Tobias Schwinger <tschwinger@isonews2.com>
Date: Sat, 22 Jul 2006 15:08:37 +0000
Subject: [PATCH] makes begin< int_<I> > return void_

[SVN r34669]
---
 include/boost/mpl/aux_/begin_end_impl.hpp | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/boost/mpl/aux_/begin_end_impl.hpp b/include/boost/mpl/aux_/begin_end_impl.hpp
index 7fb10b2..9fa6912 100644
--- a/include/boost/mpl/aux_/begin_end_impl.hpp
+++ b/include/boost/mpl/aux_/begin_end_impl.hpp
@@ -17,12 +17,29 @@
 #include <boost/mpl/begin_end_fwd.hpp>
 #include <boost/mpl/sequence_tag_fwd.hpp>
 #include <boost/mpl/void.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/aux_/has_begin.hpp>
 #include <boost/mpl/aux_/na.hpp>
 #include <boost/mpl/aux_/traits_lambda_spec.hpp>
 #include <boost/mpl/aux_/config/eti.hpp>
 
 namespace boost { namespace mpl {
 
+namespace aux { 
+
+template< typename Sequence > 
+struct begin_type 
+{ 
+    typedef typename Sequence::begin type; 
+};
+template< typename Sequence > 
+struct end_type
+{ 
+    typedef typename Sequence::end type; 
+};
+
+}
+
 // default implementation; conrete sequences might override it by 
 // specializing either the 'begin_impl/end_impl' or the primary 
 // 'begin/end' templates
@@ -32,7 +49,8 @@ struct begin_impl
 {
     template< typename Sequence > struct apply
     {
-        typedef typename Sequence::begin type;
+        typedef typename eval_if<aux::has_begin<Sequence, true_>,
+                                 aux::begin_type<Sequence>, void_>::type type;
     };
 };
 
@@ -41,7 +59,8 @@ struct end_impl
 {
     template< typename Sequence > struct apply
     {
-        typedef typename Sequence::end type;
+        typedef typename eval_if<aux::has_begin<Sequence, true_>,
+                                 aux::end_type<Sequence>, void_>::type type;
     };
 };