Spirit X3 unused

[SVN r85769]

include/boost/spirit/home/x3/support/unused.hpp

@@ -0,0 +1,93 @@
+/*=============================================================================
+    Copyright (c) 2001-2013 Joel de Guzman
+    Copyright (c) 2001-2011 Hartmut Kaiser
+
+    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)
+==============================================================================*/
+#if !defined(BOOST_SPIRIT_X3_UNUSED_APRIL_16_2006_0616PM)
+#define BOOST_SPIRIT_X3_UNUSED_APRIL_16_2006_0616PM
+
+#if defined(_MSC_VER)
+#pragma once
+#endif
+
+#include <ostream>
+#include <istream>
+#include <boost/mpl/identity.hpp>
+
+#if defined(BOOST_MSVC)
+# pragma warning(push)
+# pragma warning(disable: 4522) // multiple assignment operators specified warning
+#endif
+
+///////////////////////////////////////////////////////////////////////////////
+namespace boost { namespace spirit { namespace x3
+{
+    struct unused_type
+    {
+        unused_type()
+        {
+        }
+
+        template <typename T>
+        unused_type(T const&)
+        {
+        }
+
+        template <typename T>
+        unused_type const&
+        operator=(T const&) const
+        {
+            return *this;
+        }
+
+        template <typename T>
+        unused_type&
+        operator=(T const&)
+        {
+            return *this;
+        }
+
+        unused_type const&
+        operator=(unused_type const&) const
+        {
+            return *this;
+        }
+
+        unused_type&
+        operator=(unused_type const&)
+        {
+            return *this;
+        }
+
+        // unused_type can also masquerade as an empty context (see context.hpp)
+
+        template <typename ID>
+        struct get_result : mpl::identity<unused_type> {};
+
+        template <typename ID>
+        unused_type get(ID) const
+        {
+            return unused_type();
+        }
+    };
+
+    unused_type const unused = unused_type();
+
+    inline std::ostream& operator<<(std::ostream& out, unused_type const&)
+    {
+        return out;
+    }
+
+    inline std::istream& operator>>(std::istream& in, unused_type&)
+    {
+        return in;
+    }
+}}}
+
+#if defined(BOOST_MSVC)
+# pragma warning(pop)
+#endif
+
+#endif