From c6831e83ddedc7d86c6277a7d104f56e6548f931 Mon Sep 17 00:00:00 2001
From: Daniel Pfeifer <daniel@pfeifer-mail.de>
Date: Thu, 28 Aug 2014 12:02:47 +0200
Subject: [PATCH] karma: support boost::recursive_wrapper

---
 include/boost/spirit/home/karma/detail/extract_from.hpp | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/include/boost/spirit/home/karma/detail/extract_from.hpp b/include/boost/spirit/home/karma/detail/extract_from.hpp
index 558d056352..9ef807886d 100644
--- a/include/boost/spirit/home/karma/detail/extract_from.hpp
+++ b/include/boost/spirit/home/karma/detail/extract_from.hpp
@@ -18,6 +18,7 @@
 
 #include <boost/ref.hpp>
 #include <boost/optional.hpp>
+#include <boost/variant/recursive_wrapper.hpp>
 
 ///////////////////////////////////////////////////////////////////////////////
 namespace boost { namespace spirit { namespace traits
@@ -116,6 +117,19 @@ namespace boost { namespace spirit { namespace traits
         }
     };
 
+    // This handles recursive variants.
+    template <typename Attribute, typename Exposed>
+    struct extract_from_attribute<recursive_wrapper<Attribute>, Exposed>
+    {
+        typedef Attribute const& type;
+
+        template <typename Context>
+        static type call(recursive_wrapper<Attribute> const& attr, Context& ctx)
+        {
+            return extract_from<Exposed>(attr.get(), ctx);
+        }
+    };
+
     ///////////////////////////////////////////////////////////////////////////
     template <typename Attribute, typename Exposed, typename Enable>
     struct extract_from_container