Added boost header

test/external/boost/proto/context/null.hpp

@@ -0,0 +1,56 @@
+///////////////////////////////////////////////////////////////////////////////
+/// \file null.hpp
+/// Definintion of null_context\<\>, an evaluation context for
+/// proto::eval() that simply evaluates each child expression, doesn't
+/// combine the results at all, and returns void.
+//
+//  Copyright 2008 Eric Niebler. 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_PROTO_CONTEXT_NULL_HPP_EAN_06_24_2007
+#define BOOST_PROTO_CONTEXT_NULL_HPP_EAN_06_24_2007
+
+#include <boost/preprocessor/iteration/iterate.hpp>
+#include <boost/preprocessor/repetition/repeat.hpp>
+#include <boost/proto/proto_fwd.hpp>
+#include <boost/proto/eval.hpp>
+#include <boost/proto/traits.hpp>
+
+namespace boost { namespace proto { namespace context
+{
+
+    template<
+        typename Expr
+      , typename Context
+      , long Arity          // = Expr::proto_arity_c
+    >
+    struct null_eval
+    {};
+
+    template<typename Expr, typename Context>
+    struct null_eval<Expr, Context, 0>
+    {
+        typedef void result_type;
+        void operator()(Expr &, Context &) const
+        {}
+    };
+
+    // Additional specializations generated by the preprocessor
+    #include <boost/proto/context/detail/null_eval.hpp>
+
+    /// null_context
+    ///
+    struct null_context
+    {
+        /// null_context::eval
+        ///
+        template<typename Expr, typename ThisContext = null_context const>
+        struct eval
+          : null_eval<Expr, ThisContext>
+        {};
+    };
+
+}}}
+
+#endif