From 0f34b3a692924148440f40bcdb4d412611d503ef Mon Sep 17 00:00:00 2001
From: Joel de Guzman <djowel@gmail.com>
Date: Tue, 18 Nov 2014 23:11:13 +0800
Subject: [PATCH] Fixed C++11 implementation of map's result_of::deref_data to
 return a reference as expected.

---
 doc/iterator.qbk                                    | 11 +++++------
 include/boost/fusion/container/map/map_iterator.hpp |  6 ++++--
 test/sequence/map.cpp                               |  9 +++++++++
 3 files changed, 18 insertions(+), 8 deletions(-)

diff --git a/doc/iterator.qbk b/doc/iterator.qbk
index c4f2c741..50430a4d 100644
--- a/doc/iterator.qbk
+++ b/doc/iterator.qbk
@@ -513,7 +513,7 @@ Deferences the data property associated with the element referenced by an associ
     #include <boost/fusion/include/deref_data.hpp>
 
 [heading Example]
-    typedef __map__<__pair__<float,int&> > map;
+    typedef __map__<__pair__<float, int&> > map;
 
     int i(0);
     map m(1.0f,i);
@@ -1070,14 +1070,13 @@ Returns the type that will be returned by dereferencing the data property refere
     #include <boost/fusion/include/deref_data.hpp>
 
 [heading Example]
-    typedef __map__<__pair__<float,int> > map;
-    typedef __result_of_begin__<vec>::type first;
-
-    BOOST_MPL_ASSERT((boost::is_same<__result_of_deref_data__<first>::type, int&>));
+    typedef map<pair<float, int> > map_type;
+    typedef boost::fusion::result_of::begin<map_type>::type i_type;
+    typedef boost::fusion::result_of::deref_data<i_type>::type r_type;
+    BOOST_STATIC_ASSERT((boost::is_same<r_type, int&>::value));
 
 [endsect]
 
 [endsect]
 
 [endsect]
-
diff --git a/include/boost/fusion/container/map/map_iterator.hpp b/include/boost/fusion/container/map/map_iterator.hpp
index db89738e..03242026 100644
--- a/include/boost/fusion/container/map/map_iterator.hpp
+++ b/include/boost/fusion/container/map/map_iterator.hpp
@@ -83,8 +83,10 @@ namespace boost { namespace fusion
         {
             typedef typename Iterator::sequence sequence;
             typedef typename Iterator::index index;
-            typedef
-                decltype(boost::declval<sequence>().get(index()).second)
+            typedef typename
+                add_reference<
+                    decltype(boost::declval<sequence>().get(index()).second)
+                >::type
             type;
 
             BOOST_FUSION_GPU_ENABLED
diff --git a/test/sequence/map.cpp b/test/sequence/map.cpp
index 925d6720..9e4ecafb 100644
--- a/test/sequence/map.cpp
+++ b/test/sequence/map.cpp
@@ -139,6 +139,15 @@ main()
         pair<int, copy_all> p1;
         pair<int, copy_all> p2 = p1;
     }
+    
+    {
+        // compile test only
+        // make sure result_of::deref_data returns a reference
+        typedef map<pair<float, int> > map_type;
+        typedef boost::fusion::result_of::begin<map_type>::type i_type;
+        typedef boost::fusion::result_of::deref_data<i_type>::type r_type;
+        BOOST_STATIC_ASSERT((boost::is_same<r_type, int&>::value));
+    }
 
     return boost::report_errors();
 }