phoenix/core/is_value.hpp New file

include/boost/phoenix/core/is_value.hpp

@@ -0,0 +1,54 @@
+/*==============================================================================
+    Copyright (c) 2005-2010 Joel de Guzman
+    Copyright (c) 2015 John Fletcher
+
+    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_PHOENIX_CORE_IS_VALUE_HPP
+#define BOOST_PHOENIX_CORE_IS_VALUE_HPP
+
+#include <boost/mpl/bool.hpp>
+
+// Copied from is_actor.hpp
+
+// Note to Thomas and any future maintainer: please make this as
+// lightweight as possible (as it is right now).
+
+namespace boost { namespace phoenix
+{
+///////////////////////////////////////////////////////////////////////////////
+//
+//  is_value<T>
+//
+//      Tests if T is a value. Evaluates to mpl::true_ or mpl::false_
+//
+///////////////////////////////////////////////////////////////////////////////
+
+    namespace expression {
+        template <typename T>
+        struct value;
+    }
+
+    template <typename T, typename Enable = void>
+    struct is_value
+        : mpl::false_
+    {};
+
+    template <typename T>
+    struct is_value<T const>
+        : is_value<T>
+    {};
+
+    template <typename T>
+    struct is_value<T &>
+        : is_value<T>
+    {};
+
+    template <typename T>
+    struct is_value<expression::value<T> >
+        : mpl::true_
+    {};
+  }}
+
+#endif