From a56348497fefaf0b64b0fec36902f8d29b1d2d46 Mon Sep 17 00:00:00 2001
From: Tobias Schwinger <tschwinger@isonews2.com>
Date: Thu, 15 Feb 2007 23:28:40 +0000
Subject: [PATCH] adds O(1) empty implementation

[SVN r36963]
---
 .../fusion/sequence/container/list/cons.hpp   |  1 +
 .../container/list/detail/empty_impl.hpp      | 38 +++++++++++++++++++
 2 files changed, 39 insertions(+)
 create mode 100644 include/boost/fusion/sequence/container/list/detail/empty_impl.hpp

diff --git a/include/boost/fusion/sequence/container/list/cons.hpp b/include/boost/fusion/sequence/container/list/cons.hpp
index 075bee7d..a44e0e23 100644
--- a/include/boost/fusion/sequence/container/list/cons.hpp
+++ b/include/boost/fusion/sequence/container/list/cons.hpp
@@ -19,6 +19,7 @@
 #include <boost/fusion/sequence/container/list/detail/end_impl.hpp>
 #include <boost/fusion/sequence/container/list/detail/at_impl.hpp>
 #include <boost/fusion/sequence/container/list/detail/value_at_impl.hpp>
+#include <boost/fusion/sequence/container/list/detail/empty_impl.hpp>
 #include <boost/type_traits/is_convertible.hpp>
 #include <boost/utility/enable_if.hpp>
 #include <boost/fusion/support/sequence_base.hpp>
diff --git a/include/boost/fusion/sequence/container/list/detail/empty_impl.hpp b/include/boost/fusion/sequence/container/list/detail/empty_impl.hpp
new file mode 100644
index 00000000..4615fd40
--- /dev/null
+++ b/include/boost/fusion/sequence/container/list/detail/empty_impl.hpp
@@ -0,0 +1,38 @@
+/*=============================================================================
+    Copyright (c) 2007 Tobias Schwinger
+
+    Use, modification and distribution is subject to 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_FUSION_SEQUENCE_EMPTY_IMPL_HPP_INCLUDED)
+#define BOOST_FUSION_SEQUENCE_EMPTY_IMPL_HPP_INCLUDED
+
+#include <boost/type_traits/is_convertible.hpp>
+
+namespace boost { namespace fusion
+{
+    struct cons_tag;
+
+    struct nil;
+
+    template <typename Car, typename Cdr>
+    struct cons;
+
+    namespace extension
+    {
+        template <typename Tag>
+        struct empty_impl;
+
+        template <>
+        struct empty_impl<cons_tag>
+        {
+            template <typename Sequence>
+            struct apply
+                : boost::is_convertible<Sequence, nil>
+            {};
+        };
+    }
+}}
+
+#endif