Revert "Remove unnecessary overloads, state should always be const."

This reverts commit 9b77c26a24.

As discussed on github, the original code was wrong.

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

@@ -194,6 +194,30 @@ namespace boost { namespace fusion
     {
         return detail::BOOST_FUSION_FOLD_NAME<Seq const, State const, F>(seq, state, f);
     }
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::BOOST_FUSION_FOLD_NAME<
+        Seq
+      , State const
+      , F
+    >::type
+    BOOST_FUSION_FOLD_NAME(Seq& seq, State& state, F f)
+    {
+        return detail::BOOST_FUSION_FOLD_NAME<Seq, State, F>(seq, state, f);
+    }
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::BOOST_FUSION_FOLD_NAME<
+        Seq const
+      , State const
+      , F
+    >::type
+    BOOST_FUSION_FOLD_NAME(Seq const& seq, State& state, F f)
+    {
+        return detail::BOOST_FUSION_FOLD_NAME<Seq const, State, F>(seq, state, f);
+    }
 }}
 
 #undef BOOST_FUSION_FOLD_NAME

include/boost/fusion/algorithm/iteration/fold_fwd.hpp

@@ -33,6 +33,24 @@ namespace boost { namespace fusion
       , F
     >::type
     fold(Seq const& seq, State const& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::fold<
+        Seq
+      , State const
+      , F
+    >::type
+    fold(Seq& seq, State& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::fold<
+        Seq const
+      , State const
+      , F
+    >::type
+    fold(Seq const& seq, State& state, F f);
 }}
 
 #endif

include/boost/fusion/algorithm/iteration/iter_fold_fwd.hpp

@@ -33,6 +33,24 @@ namespace boost { namespace fusion
       , F
     >::type
     iter_fold(Seq const& seq, State const& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::iter_fold<
+        Seq
+      , State const
+      , F
+    >::type
+    iter_fold(Seq& seq, State& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::iter_fold<
+        Seq const
+      , State const
+      , F
+    >::type
+    iter_fold(Seq const& seq, State& state, F f);
 }}
 
 #endif

include/boost/fusion/algorithm/iteration/reverse_fold_fwd.hpp

@@ -33,6 +33,24 @@ namespace boost { namespace fusion
       , F
     >::type
     reverse_fold(Seq const& seq, State const& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::reverse_fold<
+        Seq
+      , State const
+      , F
+    >::type
+    reverse_fold(Seq& seq, State& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::reverse_fold<
+        Seq const
+      , State const
+      , F
+    >::type
+    reverse_fold(Seq const& seq, State& state, F f);
 }}
 
 #endif

include/boost/fusion/algorithm/iteration/reverse_iter_fold_fwd.hpp

@@ -33,6 +33,24 @@ namespace boost { namespace fusion
       , F
     >::type
     reverse_iter_fold(Seq const& seq, State const& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::reverse_iter_fold<
+        Seq
+      , State const
+      , F
+    >::type
+    reverse_iter_fold(Seq& seq, State& state, F f);
+
+    template<typename Seq, typename State, typename F>
+    BOOST_CONSTEXPR BOOST_FUSION_GPU_ENABLED
+    inline typename result_of::reverse_iter_fold<
+        Seq const
+      , State const
+      , F
+    >::type
+    reverse_iter_fold(Seq const& seq, State& state, F f);
 }}
 
 #endif