fusion fold and transform passing refs for lvalues as per result_of protocol

[SVN r38039]

include/boost/fusion/algorithm/iteration/detail/fold.hpp

@@ -13,6 +13,9 @@
 #include <boost/fusion/iterator/distance.hpp>
 #include <boost/utility/result_of.hpp>
 
+#include <boost/type_traits/add_const.hpp>
+#include <boost/type_traits/add_reference.hpp>
+
 namespace boost { namespace fusion {
 namespace result_of
 {
@@ -32,8 +35,11 @@ namespace detail
 
     template <typename Iterator, typename State, typename F>
     struct fold_apply
-        : boost::result_of<F(typename result_of::value_of<Iterator>::type, State)>
+    {
-    {};
+        typedef typename result_of::deref<Iterator>::type dereferenced;
+        typedef typename add_reference<typename add_const<State>::type>::type lvalue_state;
+        typedef typename boost::result_of<F(dereferenced, lvalue_state)>::type type;
+    };
 
     template <typename First, typename Last, typename State, typename F>
     struct static_fold;

include/boost/fusion/algorithm/transformation/detail/replace.hpp

@@ -9,6 +9,7 @@
 
 #include <boost/type_traits/is_convertible.hpp>
 #include <boost/mpl/if.hpp>
+#include <boost/type_traits/remove_reference.hpp>
 
 namespace boost { namespace fusion { namespace detail
 {
@@ -43,14 +44,15 @@ namespace boost { namespace fusion { namespace detail
         replacer(T const& old_value, T const& new_value)
             : old_value(old_value), new_value(new_value) {}
 
-        template<typename Params>
+        template<typename Sig>
         struct result;
 
         template <typename U1, typename U2>
         struct result<replacer<U1>(U2)>
         {
+            typedef typename remove_reference<U2>::type value;
             typedef typename
-                mpl::if_<is_convertible<T, U2>, U2, U2 const&>::type
+                mpl::if_<is_convertible<T, value>, value, value const&>::type
             type;
         };
     

include/boost/fusion/algorithm/transformation/detail/replace_if.hpp

@@ -9,6 +9,7 @@
 
 #include <boost/utility/enable_if.hpp>
 #include <boost/mpl/if.hpp>
+#include <boost/type_traits/remove_reference.hpp>
 
 namespace boost { namespace fusion { namespace detail
 {
@@ -49,8 +50,9 @@ namespace boost { namespace fusion { namespace detail
         template <typename F1, typename T1, typename U>
         struct result<replacer_if<F1, T1>(U)>
         {
+            typedef typename remove_reference<U>::type value;
             typedef typename
-                mpl::if_<is_convertible<T, U>, U, U const&>::type
+                mpl::if_<is_convertible<T, value>, value, value const&>::type
             type;
         };
     

include/boost/fusion/sequence/view/transform_view/detail/deref_impl.hpp

@@ -30,7 +30,7 @@ namespace boost { namespace fusion
             struct apply
             {
                 typedef typename
-                    result_of::value_of<typename Iterator::first_type>::type
+                    result_of::deref<typename Iterator::first_type>::type
                 value_type;
 
                 typedef detail::apply_transform_result<typename Iterator::transform_type> transform_type;
@@ -52,10 +52,10 @@ namespace boost { namespace fusion
             struct apply
             {
                 typedef typename
-                    result_of::value_of<typename Iterator::first1_type>::type
+                    result_of::deref<typename Iterator::first1_type>::type
                 value1_type;
                 typedef typename
-                    result_of::value_of<typename Iterator::first2_type>::type
+                    result_of::deref<typename Iterator::first2_type>::type
                 value2_type;
 
                 typedef detail::apply_transform_result<typename Iterator::transform_type> transform_type;

include/boost/fusion/sequence/view/zip_view/detail/advance_impl.hpp

@@ -11,6 +11,7 @@
 #include <boost/fusion/sequence/view/zip_view/zip_view_iterator_fwd.hpp>
 #include <boost/fusion/iterator/advance.hpp>
 #include <boost/fusion/algorithm/transformation/transform.hpp>
+#include <boost/type_traits/remove_reference.hpp>
 
 namespace boost { namespace fusion {
 
@@ -21,13 +22,15 @@ namespace boost { namespace fusion {
         template<typename N>
         struct poly_advance
         {
-            template<typename T>
+            template<typename Sig>
             struct result;
 
             template<typename N1, typename It>
             struct result<poly_advance<N1>(It)>
-                : result_of::advance<It,N>
+            {
-            {};
+                typedef typename remove_reference<It>::type it;
+                typedef typename result_of::advance<it,N>::type type;
+            };
 
             template<typename It>
             typename result<poly_advance(It)>::type

include/boost/fusion/sequence/view/zip_view/detail/deref_impl.hpp

@@ -16,6 +16,8 @@
 #include <boost/mpl/eval_if.hpp>
 #include <boost/mpl/identity.hpp>
 #include <boost/type_traits/is_same.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/remove_const.hpp>
 
 namespace boost { namespace fusion {
 
@@ -25,15 +27,19 @@ namespace boost { namespace fusion {
     {
         struct poly_deref
         {
-            template<typename T>
+            template<typename Sig>
             struct result;
 
             template<typename It>
             struct result<poly_deref(It)>
-                : mpl::eval_if<is_same<It, unused_type>,
+            {
-                               mpl::identity<unused_type>,
+                typedef typename remove_const<
-                               result_of::deref<It> >
+                    typename remove_reference<It>::type>::type it;
-            {};
+
+                typedef typename mpl::eval_if<is_same<it, unused_type>,
+                    mpl::identity<unused_type>,
+                    result_of::deref<it> >::type type;
+            };
 
             template<typename It>
             typename result<poly_deref(It)>::type

include/boost/fusion/sequence/view/zip_view/detail/next_impl.hpp

@@ -15,6 +15,8 @@
 #include <boost/mpl/eval_if.hpp>
 #include <boost/mpl/identity.hpp>
 #include <boost/type_traits/is_same.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/remove_const.hpp>
 
 namespace boost { namespace fusion {
 
@@ -24,15 +26,19 @@ namespace boost { namespace fusion {
     {
         struct poly_next
         {
-            template<typename T>
+            template<typename Sig>
             struct result;
 
             template<typename It>
             struct result<poly_next(It)>
-                : mpl::eval_if<is_same<It, unused_type>,
+            {
-                               mpl::identity<unused_type>,
+                typedef typename remove_const<
-                               result_of::next<It> >
+                    typename remove_reference<It>::type>::type it;
-            {};
+
+                typedef typename mpl::eval_if<is_same<it, unused_type>,
+                    mpl::identity<unused_type>,
+                    result_of::next<it> >::type type;
+            };
 
             template<typename It>
             typename result<poly_next(It)>::type

include/boost/fusion/sequence/view/zip_view/detail/prior_impl.hpp

@@ -15,6 +15,8 @@
 #include <boost/mpl/eval_if.hpp>
 #include <boost/mpl/identity.hpp>
 #include <boost/type_traits/is_same.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/remove_const.hpp>
 
 namespace boost { namespace fusion {
 
@@ -24,15 +26,18 @@ namespace boost { namespace fusion {
     {
         struct poly_prior
         {
-            template<typename T>
+            template<typename Sig>
             struct result;
 
             template<typename It>
             struct result<poly_prior(It)>
-                : mpl::eval_if<is_same<It, unused_type>,
+            {
-                               mpl::identity<unused_type>,
+                typedef typename remove_const<
-                               result_of::prior<It> >
+                    typename remove_reference<It>::type>::type it;
-            {};
+                typedef typename mpl::eval_if<is_same<it, unused_type>,
+                    mpl::identity<unused_type>,
+                    result_of::prior<it> >::type type;
+            };
 
             template<typename It>
             typename result<poly_prior(It)>::type

include/boost/fusion/sequence/view/zip_view/detail/strictest_traversal.hpp

@@ -39,15 +39,17 @@ namespace boost { namespace fusion {
 
         struct strictest_traversal_impl
         {
-            template<typename T>
+            template<typename Sig>
             struct result;
 
             template<typename Next, typename StrictestSoFar>
             struct result<strictest_traversal_impl(Next, StrictestSoFar)>
             {
-                typedef StrictestSoFar tag1;
+                typedef typename remove_reference<Next>::type next_value;
-                typedef typename traits::category_of<
+                typedef typename remove_reference<StrictestSoFar>::type strictest_so_far;
-                    typename remove_reference<Next>::type>::type tag2;
+
+                typedef strictest_so_far tag1;
+                typedef typename traits::category_of<next_value>::type tag2;
 
                 typedef typename stricter_traversal<tag1,tag2>::type type;
             };

include/boost/fusion/sequence/view/zip_view/zip_view.hpp

@@ -73,8 +73,11 @@ namespace boost { namespace fusion {
 
             template<typename Lhs, typename Rhs>
             struct result<poly_min(Lhs, Rhs)>
-                : mpl::min<Lhs, Rhs>
+            {
-            {};
+                typedef typename remove_reference<Lhs>::type lhs;
+                typedef typename remove_reference<Rhs>::type rhs;
+                typedef typename mpl::min<lhs, rhs>::type type;
+            };
         };
 
         template<typename Sequences>

test/Jamfile

@@ -145,4 +145,3 @@ import testing ;
     run sequence/ext_/iterator_range_s.cpp ;
     explicit iterator_range_s ;
 }
-

test/algorithm/fold.cpp

@@ -19,6 +19,10 @@
 #include <boost/mpl/int.hpp>
 #include <boost/mpl/vector.hpp>
 
+#include <boost/type_traits/remove_const.hpp>
+#include <boost/type_traits/remove_reference.hpp>
+#include <boost/type_traits/is_reference.hpp>
+
 #include <string>
 
 using boost::mpl::if_;
@@ -33,7 +37,8 @@ struct add_ints_only
     template <typename T, typename State>
     struct result<add_ints_only(T,State)>
     {
-        typedef State type;
+        typedef typename boost::remove_const<
+            typename boost::remove_reference<State>::type>::type type;
     };
 
     template <typename T, typename State>
@@ -58,11 +63,16 @@ struct count_ints
     template <typename T, typename CountT>
     struct result<count_ints(T,CountT)>
     {
+        typedef typename boost::remove_const<
+            typename boost::remove_reference<T>::type>::type elem;
+        typedef typename boost::remove_const<
+            typename boost::remove_reference<CountT>::type>::type state;
+
         typedef typename
             if_<
-                is_same<T, int>
+                is_same<elem, int>
-              , typename boost::mpl::next<CountT>::type
+              , typename boost::mpl::next<state>::type
-              , CountT
+              , state
             >::type
         type;
     };
@@ -86,6 +96,25 @@ struct appender
     }
 };
 
+struct lvalue_adder
+{
+    template<typename Sig>
+    struct result;
+
+    template<typename T0, typename T1>
+    struct result<lvalue_adder(T0&, T1)>
+    {
+        // Second argument still needs to support rvalues - see definition of fusion::fold
+        typedef T0 type; 
+    };
+
+    template<typename T0, typename T1>
+    T0 operator()(T0& lhs, T1 const& rhs) const
+    {
+        return lhs + rhs;
+    }
+};
+
 int
 main()
 {
@@ -130,6 +159,11 @@ main()
                    == "abcde");
     }
 
+    {
+        vector<int, int> vec(1,2);
+        BOOST_TEST(fusion::fold(vec, 0, lvalue_adder()) == 3);
+    }
+
     {
         typedef vector<int, char, int, double> vector_type;
         vector_type v(12345, 'x', 678910, 3.36);

test/algorithm/transform.cpp

@@ -19,13 +19,12 @@
 
 struct square
 {
-    template<typename T>
+    template<typename Sig>
     struct result;
 
     template <typename T>
     struct result<square(T)>
     {
-        BOOST_STATIC_ASSERT(!boost::is_reference<T>::value);
         typedef int type;
     };
 
@@ -38,7 +37,7 @@ struct square
 
 struct add
 {
-    template<typename T>
+    template<typename Sig>
     struct result;
 
     template <typename A, typename B>
@@ -54,6 +53,42 @@ struct add
     }
 };
 
+struct unary_lvalue_transform
+{
+    template<typename Sig>
+    struct result;
+
+    template<typename T>
+    struct result<unary_lvalue_transform(T&)>
+    {
+        typedef T* type;
+    };
+
+    template<typename T>
+    T* operator()(T& t) const
+    {
+        return &t;
+    }
+};
+
+struct binary_lvalue_transform
+{
+    template<typename Sig>
+    struct result;
+
+    template<typename T0, typename T1>
+    struct result<binary_lvalue_transform(T0&,T1&)>
+    {
+        typedef T0* type;
+    };
+
+    template<typename T0, typename T1>
+    T0* operator()(T0& t0, T1&) const
+    {
+        return &t0;
+    }
+};
+
 int
 main()
 {
@@ -92,6 +127,20 @@ main()
         BOOST_TEST((transform(tup1, tup2, add()) == make_vector(5, 7, 9)));
     }
 
+    {
+        // Unary transform that requires lvalues, just check compilation
+        vector<int, int, int> tup1(1, 2, 3);
+        BOOST_TEST(at_c<0>(transform(tup1, unary_lvalue_transform())) == &at_c<0>(tup1));
+        BOOST_TEST(*begin(transform(tup1, unary_lvalue_transform())) == &at_c<0>(tup1));
+    }
+
+    {
+        vector<int, int, int> tup1(1, 2, 3);
+        vector<int, int, int> tup2(4, 5, 6);
+        BOOST_TEST(at_c<0>(transform(tup1, tup2, binary_lvalue_transform())) == &at_c<0>(tup1));
+        BOOST_TEST(*begin(transform(tup1, tup2, binary_lvalue_transform())) == &at_c<0>(tup1));
+    }
+
     return boost::report_errors();
 }