From c15dd57405bb39b2147c0152e4fe3a7edcba0d10 Mon Sep 17 00:00:00 2001
From: Christopher Schmidt <mr.chr.schmidt@online.de>
Date: Sun, 19 Dec 2010 18:35:52 +0000
Subject: [PATCH] Fusion: mask fusion::begin/fusion::end with SFINAE, fixes
 #4028

[SVN r67352]
---
 include/boost/fusion/sequence/intrinsic/begin.hpp | 14 ++++++++++++--
 include/boost/fusion/sequence/intrinsic/end.hpp   | 14 ++++++++++++--
 2 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/include/boost/fusion/sequence/intrinsic/begin.hpp b/include/boost/fusion/sequence/intrinsic/begin.hpp
index 5dbe0c40..c9ece3ab 100644
--- a/include/boost/fusion/sequence/intrinsic/begin.hpp
+++ b/include/boost/fusion/sequence/intrinsic/begin.hpp
@@ -8,6 +8,8 @@
 #define FUSION_BEGIN_04052005_1132
 
 #include <boost/fusion/support/tag_of.hpp>
+#include <boost/fusion/support/is_sequence.hpp>
+#include <boost/utility/enable_if.hpp>
 
 namespace boost { namespace fusion
 {
@@ -57,14 +59,22 @@ namespace boost { namespace fusion
     }
 
     template <typename Sequence>
-    inline typename result_of::begin<Sequence>::type const
+    inline typename
+        lazy_enable_if<
+            traits::is_sequence<Sequence>
+          , result_of::begin<Sequence>
+        >::type const
     begin(Sequence& seq)
     {
         return result_of::begin<Sequence>::call(seq);
     }
 
     template <typename Sequence>
-    inline typename result_of::begin<Sequence const>::type const
+    inline typename
+        lazy_enable_if<
+            traits::is_sequence<Sequence>
+          , result_of::begin<Sequence const>
+        >::type const
     begin(Sequence const& seq)
     {
         return result_of::begin<Sequence const>::call(seq);
diff --git a/include/boost/fusion/sequence/intrinsic/end.hpp b/include/boost/fusion/sequence/intrinsic/end.hpp
index 98a554e3..02476710 100644
--- a/include/boost/fusion/sequence/intrinsic/end.hpp
+++ b/include/boost/fusion/sequence/intrinsic/end.hpp
@@ -8,6 +8,8 @@
 #define FUSION_END_04052005_1141
 
 #include <boost/fusion/support/tag_of.hpp>
+#include <boost/fusion/support/is_sequence.hpp>
+#include <boost/utility/enable_if.hpp>
 
 namespace boost { namespace fusion
 {
@@ -57,14 +59,22 @@ namespace boost { namespace fusion
     }
 
     template <typename Sequence>
-    inline typename result_of::end<Sequence>::type const
+    inline typename
+        lazy_enable_if<
+            traits::is_sequence<Sequence>
+          , result_of::end<Sequence>
+        >::type const
     end(Sequence& seq)
     {
         return result_of::end<Sequence>::call(seq);
     }
 
     template <typename Sequence>
-    inline typename result_of::end<Sequence const>::type const
+    inline typename
+        lazy_enable_if<
+            traits::is_sequence<Sequence>
+          , result_of::end<Sequence const>
+        >::type const
     end(Sequence const& seq)
     {
         return result_of::end<Sequence const>::call(seq);