[Boost-commit] svn:boost r52931 - trunk/boost/spirit/home/support

Subject: [Boost-commit] svn:boost r52931 - trunk/boost/spirit/home/support
From: hartmut.kaiser_at_[hidden]
Date: 2009-05-11 22:50:42

Author: hkaiser
Date: 2009-05-11 22:50:42 EDT (Mon, 11 May 2009)
New Revision: 52931
URL: http://svn.boost.org/trac/boost/changeset/52931

Log:
Spirit: fixing a problem during attribute type calculation for qi alternatives 
Text files modified: 
   trunk/boost/spirit/home/support/attributes.hpp |    31 ++++++++++++++++++++++++-------         
   1 files changed, 24 insertions(+), 7 deletions(-)

Modified: trunk/boost/spirit/home/support/attributes.hpp
==============================================================================
--- trunk/boost/spirit/home/support/attributes.hpp	(original)
+++ trunk/boost/spirit/home/support/attributes.hpp	2009-05-11 22:50:42 EDT (Mon, 11 May 2009)
@@ -23,6 +23,7 @@
 #include <boost/type_traits/is_same.hpp>
 #include <boost/mpl/eval_if.hpp>
 #include <boost/mpl/end.hpp>
+#include <boost/mpl/equal_to.hpp>
 #include <boost/mpl/find_if.hpp>
 #include <boost/mpl/identity.hpp>
 #include <boost/variant.hpp>
@@ -255,15 +256,17 @@
             filter_unused_attributes<Sequence>::type
         filtered_attributes;
 
+        typedef has_no_unused<Sequence> has_no_unused_type;
+
         // If the original attribute list does not contain any unused
         // attributes, it is used, otherwise a single unused_type is
         // pushed to the front of the list. This is to make sure that if
         // there is an unused_type in the list, it is the first one.
         typedef typename
             mpl::eval_if<
-                has_no_unused<Sequence>,
-                mpl::identity<Sequence>,
-                fusion::result_of::push_front<filtered_attributes, unused_type>
+                has_no_unused_type
+              , mpl::identity<Sequence>
+              , fusion::result_of::push_front<filtered_attributes, unused_type>
             >::type
         attribute_sequence;
 
@@ -278,13 +281,27 @@
             >::type
         new_sequence;
 
+        // If there is only an unused_type and one other type in the list of 
+        // types we strip off the variant. IOTW, we collapse single element 
+        // variants, variant<unused_type, T> to T.
+        typedef typename
+            mpl::eval_if<
+                mpl::and_<
+                    mpl::equal_to<mpl::size<new_sequence>, mpl::int_<2> >
+                  , mpl::not_<has_no_unused_type> >
+              , fusion::result_of::pop_front<new_sequence>
+              , mpl::identity<new_sequence>
+            >::type
+        shortened_type;
+
         // If there is only one type in the list of types we strip off the
-        // variant. IOTW, collapse single element variants, variant<T> to T.
+        // variant as well. IOTW, we collapse single element variants, 
+        // variant<T> to T.
         typedef typename
             mpl::eval_if<
-                mpl::equal_to<mpl::size<new_sequence>, mpl::int_<1> >,
-                mpl::deref<mpl::front<attribute_sequence> >,
-                spirit::detail::as_variant<new_sequence>
+                mpl::equal_to<mpl::size<shortened_type>, mpl::int_<1> >,
+                mpl::front<shortened_type>,
+                spirit::detail::as_variant<shortened_type>
             >::type
         type;
     };