From aa7b0a697229305f12d89ba3f17b4ce9f909519d Mon Sep 17 00:00:00 2001
From: "Damien Buhl (alias daminetreg)" <damien.buhl@lecbna.org>
Date: Tue, 23 Sep 2014 23:07:00 +0200
Subject: [PATCH] Factoring out the workaround to access last variadic
 parameter.

Indeed when some parameter are BOOST_PP_EMPTY the last parameter is
accessed correctly but results in a compilation error which doesn't stop
some compiler (e.g. g++) to go through the preprocessing pass and still
compile the binary correctly. But to avoid the error message I used a
workaround which behaves better. I preferred factoring it out to make
clear that there are some reason why this element is strangely accessed.
---
 .../adapted/adt/detail/adapt_base_attr_filler.hpp      | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/boost/fusion/adapted/adt/detail/adapt_base_attr_filler.hpp b/include/boost/fusion/adapted/adt/detail/adapt_base_attr_filler.hpp
index e88d7f1e..09bd4014 100644
--- a/include/boost/fusion/adapted/adt/detail/adapt_base_attr_filler.hpp
+++ b/include/boost/fusion/adapted/adt/detail/adapt_base_attr_filler.hpp
@@ -11,6 +11,7 @@
 #include <boost/config.hpp>
 #include <boost/fusion/adapted/struct/detail/preprocessor/is_seq.hpp>
 
+#include <boost/preprocessor/arithmetic/sub.hpp>
 #include <boost/preprocessor/control/if.hpp>
 #include <boost/preprocessor/logical/or.hpp>
 #include <boost/preprocessor/empty.hpp>
@@ -53,13 +54,18 @@
               BOOST_PP_IS_EMPTY(BOOST_PP_VARIADIC_ELEM(1, __VA_ARGS__))),       \
           BOOST_FUSION_ADAPT_ADT_WRAP_ATTR(                                     \
               BOOST_PP_VARIADIC_ELEM(2, __VA_ARGS__),                           \
-              BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_REST_N(3,                          \
-                  BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__))) ),                    \
+              BOOST_FUSION_WORKAROUND_VARIADIC_EMPTINESS_LAST_ELEM(__VA_ARGS__) \
+          ),                                                                    \
           BOOST_FUSION_ADAPT_ADT_WRAP_ATTR(__VA_ARGS__))
 
 #  define BOOST_FUSION_ADAPT_ADT_WRAP_ATTR(...)                                 \
       ((BOOST_PP_VARIADIC_SIZE(__VA_ARGS__), (__VA_ARGS__)))
 
+#  define BOOST_FUSION_WORKAROUND_VARIADIC_EMPTINESS_LAST_ELEM(...)             \
+  BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_REST_N(                                        \
+            BOOST_PP_SUB(BOOST_PP_VARIADIC_SIZE(__VA_ARGS__), 1),               \
+        BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__)))
+
 #else // BOOST_PP_VARIADICS
 
 #  define BOOST_FUSION_ADAPT_ADT_FILLER_0(A, B, C, D)                           \