Merge from trunk

[SVN r79274]

include/boost/fusion/support/as_const.hpp

@@ -0,0 +1,26 @@
+/*=============================================================================
+    Copyright (c) 2012 Nathan Ridge
+
+    Distributed under the Boost Software License, Version 1.0. (See accompanying
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+#ifndef BOOST_FUSION_SUPPORT_AS_CONST_HPP
+#define BOOST_FUSION_SUPPORT_AS_CONST_HPP
+
+namespace boost { namespace fusion { namespace extension
+{
+    // A customization point that allows certain wrappers around
+    // Fusion sequence elements (e.g. adt_attribute_proxy) to be
+    // unwrapped in contexts where the element only needs to be
+    // read. The library wraps accesses to Fusion elements in
+    // such contexts with calls to this function. Users can
+    // specialize this function for their own wrappers.
+    template <typename T>
+    const T& as_const(const T& obj)
+    {
+        return obj;
+    }
+
+}}}
+
+#endif