From a31009e73c24cb2c990c075192fe7058517b9d11 Mon Sep 17 00:00:00 2001
From: Kohei Takahashi <flast@flast.jp>
Date: Tue, 23 Jun 2015 11:17:30 +0900
Subject: [PATCH] at_key and value_at_key are aware of no-bounds sequence.

---
 .../fusion/sequence/intrinsic/at_key.hpp      | 23 +++++++++++++++--
 .../sequence/intrinsic/value_at_key.hpp       | 25 ++++++++++++++++---
 2 files changed, 43 insertions(+), 5 deletions(-)

diff --git a/include/boost/fusion/sequence/intrinsic/at_key.hpp b/include/boost/fusion/sequence/intrinsic/at_key.hpp
index 4693a905..e8fa2ade 100644
--- a/include/boost/fusion/sequence/intrinsic/at_key.hpp
+++ b/include/boost/fusion/sequence/intrinsic/at_key.hpp
@@ -11,10 +11,15 @@
 #include <boost/fusion/support/config.hpp>
 #include <boost/type_traits/is_const.hpp>
 #include <boost/fusion/sequence/intrinsic_fwd.hpp>
+#include <boost/fusion/sequence/intrinsic/has_key.hpp>
 #include <boost/fusion/algorithm/query/find.hpp>
 #include <boost/fusion/iterator/deref_data.hpp>
 #include <boost/fusion/support/tag_of.hpp>
+#include <boost/fusion/support/category_of.hpp>
 #include <boost/fusion/support/detail/access.hpp>
+#include <boost/mpl/empty_base.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/mpl/or.hpp>
 
 namespace boost { namespace fusion
 {
@@ -64,12 +69,26 @@ namespace boost { namespace fusion
         struct at_key_impl<std_pair_tag>;
     }
 
+    namespace detail
+    {
+        template <typename Sequence, typename Key, typename Tag>
+        struct at_key_impl
+            : mpl::if_<
+                  mpl::or_<
+                      typename extension::has_key_impl<Tag>::template apply<Sequence, Key>
+                    , traits::has_no_bounds<Sequence>
+                  >
+                , typename extension::at_key_impl<Tag>::template apply<Sequence, Key>
+                , mpl::empty_base
+              >::type
+        {};
+    }
+
     namespace result_of
     {
         template <typename Sequence, typename Key>
         struct at_key
-            : extension::at_key_impl<typename detail::tag_of<Sequence>::type>::
-                template apply<Sequence, Key>
+            : detail::at_key_impl<Sequence, Key, typename detail::tag_of<Sequence>::type>
         {};
     }
 
diff --git a/include/boost/fusion/sequence/intrinsic/value_at_key.hpp b/include/boost/fusion/sequence/intrinsic/value_at_key.hpp
index 6d8be3fb..8b3940e7 100644
--- a/include/boost/fusion/sequence/intrinsic/value_at_key.hpp
+++ b/include/boost/fusion/sequence/intrinsic/value_at_key.hpp
@@ -10,10 +10,15 @@
 
 #include <boost/fusion/support/config.hpp>
 #include <boost/mpl/int.hpp>
+#include <boost/mpl/empty_base.hpp>
+#include <boost/mpl/if.hpp>
+#include <boost/mpl/or.hpp>
 #include <boost/fusion/sequence/intrinsic_fwd.hpp>
+#include <boost/fusion/sequence/intrinsic/has_key.hpp>
 #include <boost/fusion/iterator/value_of_data.hpp>
 #include <boost/fusion/algorithm/query/find.hpp>
 #include <boost/fusion/support/tag_of.hpp>
+#include <boost/fusion/support/category_of.hpp>
 
 namespace boost { namespace fusion
 {
@@ -52,13 +57,27 @@ namespace boost { namespace fusion
         template <>
         struct value_at_key_impl<std_pair_tag>;
     }
-    
+
+    namespace detail
+    {
+        template <typename Sequence, typename N, typename Tag>
+        struct value_at_key_impl
+            : mpl::if_<
+                  mpl::or_<
+                      typename extension::has_key_impl<Tag>::template apply<Sequence, N>
+                    , traits::has_no_bounds<Sequence>
+                  >
+                , typename extension::value_at_key_impl<Tag>::template apply<Sequence, N>
+                , mpl::empty_base
+              >::type
+        {};
+    }
+
     namespace result_of
     {
         template <typename Sequence, typename N>
         struct value_at_key
-            : extension::value_at_key_impl<typename detail::tag_of<Sequence>::type>::
-                template apply<Sequence, N>
+            : detail::value_at_key_impl<Sequence, N, typename detail::tag_of<Sequence>::type>
         {};
     }
 }}