From b6742e3e99fdbf334df93a434bf859dd4a942532 Mon Sep 17 00:00:00 2001
From: Jonathan Turkanis <j@coderage.com>
Date: Thu, 7 Apr 2005 03:54:07 +0000
Subject: [PATCH] added overload of unwrap for const components

[SVN r28035]
---
 include/boost/iostreams/detail/wrap_unwrap.hpp | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/include/boost/iostreams/detail/wrap_unwrap.hpp b/include/boost/iostreams/detail/wrap_unwrap.hpp
index de0f1c3..87b02ac 100755
--- a/include/boost/iostreams/detail/wrap_unwrap.hpp
+++ b/include/boost/iostreams/detail/wrap_unwrap.hpp
@@ -11,7 +11,8 @@
 # pragma once
 #endif              
 
-#include <boost/config.hpp>                             // SFINAE.
+#include <boost/config.hpp>                             // SFINAE, MSVC.
+#include <boost/detail/workaround.hpp>
 #include <boost/iostreams/detail/enable_if_stream.hpp>
 #include <boost/iostreams/traits_fwd.hpp>               // is_std_io.
 #include <boost/mpl/bool.hpp>
@@ -83,6 +84,11 @@ unwrap(const reference_wrapper<T>& ref) { return ref.get(); }
 template<typename T>
 typename unwrapped_type<T>::type& unwrap(T& t) { return t; }
 
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1310)
+    template<typename T>
+    const typename unwrapped_type<T>::type& unwrap(const T& t) { return t; }
+#endif
+
 } } } // End namespaces detail, iostreams, boost.
 
 #endif // #ifndef BOOST_IOSTREAMS_DETAIL_WRAP_UNWRAP_HPP_INCLUDED //-----------------//