From 3298875eccb727291ecbafaa6c7dda9be43be557 Mon Sep 17 00:00:00 2001
From: Charly Chevalier <charly.chevalier@numscale.com>
Date: Tue, 10 Nov 2015 14:04:16 +0100
Subject: [PATCH] Add double identity trick for fast value_at (vectors)

This is a workaround to make decltype(expr)::type compiles
with old compilers.
---
 include/boost/fusion/container/vector/detail/value_at_impl.hpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/boost/fusion/container/vector/detail/value_at_impl.hpp b/include/boost/fusion/container/vector/detail/value_at_impl.hpp
index 7d134054..6c8c41fb 100644
--- a/include/boost/fusion/container/vector/detail/value_at_impl.hpp
+++ b/include/boost/fusion/container/vector/detail/value_at_impl.hpp
@@ -47,7 +47,7 @@ namespace boost { namespace fusion
             struct apply
             {
                 typedef typename boost::remove_cv<Sequence>::type seq;
-                typedef typename decltype(seq::template value_at_impl<N::value>(boost::declval<seq*>()))::type type;
+                typedef typename mpl::identity<decltype(seq::template value_at_impl<N::value>(boost::declval<seq*>()))>::type::type type;
             };
         };
     }