From d1cc519a4412ee8e350f73b15bb4ef353f9b0664 Mon Sep 17 00:00:00 2001
From: Dan Marsden <danmarsden@yahoo.co.uk>
Date: Tue, 6 Mar 2007 21:37:26 +0000
Subject: [PATCH] unused entries in zip

[SVN r37150]
---
 .../sequence/view/zip_view/detail/at_impl.hpp | 14 ++++-
 .../view/zip_view/detail/begin_impl.hpp       | 12 +++-
 .../view/zip_view/detail/deref_impl.hpp       | 13 +++-
 .../view/zip_view/detail/end_impl.hpp         | 24 ++++++-
 .../view/zip_view/detail/next_impl.hpp        | 13 +++-
 .../view/zip_view/detail/prior_impl.hpp       | 13 +++-
 .../view/zip_view/detail/value_at_impl.hpp    |  8 ++-
 .../view/zip_view/detail/value_of_impl.hpp    |  8 ++-
 .../sequence/view/zip_view/zip_view.hpp       |  7 ++-
 include/boost/fusion/support.hpp              |  1 +
 include/boost/fusion/support/unused.hpp       | 62 +++++++++++++++++++
 11 files changed, 163 insertions(+), 12 deletions(-)
 create mode 100644 include/boost/fusion/support/unused.hpp

diff --git a/include/boost/fusion/sequence/view/zip_view/detail/at_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/at_impl.hpp
index ff16e9bd..353fb5eb 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/at_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/at_impl.hpp
@@ -15,6 +15,11 @@
 #include <boost/type_traits/remove_reference.hpp>
 #include <boost/type_traits/is_reference.hpp>
 #include <boost/mpl/assert.hpp>
+#include <boost/fusion/support/unused.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
+
 
 namespace boost { namespace fusion 
 {
@@ -27,7 +32,9 @@ namespace boost { namespace fusion
         {
             template<typename SeqRef>
             struct result
-                : result_of::at<typename remove_reference<SeqRef>::type, N>
+                : mpl::eval_if<is_same<SeqRef, unused_type const&>,
+                               mpl::identity<unused_type>,
+                               result_of::at<typename remove_reference<SeqRef>::type, N> >
             {
                 BOOST_MPL_ASSERT((is_reference<SeqRef>));
             };
@@ -45,6 +52,11 @@ namespace boost { namespace fusion
             {
                 return fusion::at<N>(seq);
             }
+
+            unused_type operator()(unused_type const&) const
+            {
+                return unused_type();
+            }
         };
     }
 
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/begin_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/begin_impl.hpp
index 744052c7..37ed2a8d 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/begin_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/begin_impl.hpp
@@ -13,7 +13,11 @@
 #include <boost/fusion/algorithm/transformation/transform.hpp>
 #include <boost/type_traits/remove_reference.hpp>
 #include <boost/type_traits/is_reference.hpp>
+#include <boost/type_traits/is_same.hpp>
 #include <boost/mpl/assert.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/fusion/support/unused.hpp>
 
 namespace boost { namespace fusion {
 
@@ -25,7 +29,9 @@ namespace boost { namespace fusion {
         {
             template<typename SeqRef>
             struct result
-                : result_of::begin<typename remove_reference<SeqRef>::type>
+                : mpl::eval_if<is_same<SeqRef, unused_type const&>,
+                               mpl::identity<unused_type>,
+                               result_of::begin<typename remove_reference<SeqRef>::type> >
             {
                 BOOST_MPL_ASSERT((is_reference<SeqRef>));
             };
@@ -44,6 +50,10 @@ namespace boost { namespace fusion {
                 return fusion::begin(seq);
             }
 
+            unused_type operator()(unused_type const&) const
+            {
+                return unused_type();
+            }
         };
     }
 
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/deref_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/deref_impl.hpp
index 0d263e25..ee7399fc 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/deref_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/deref_impl.hpp
@@ -12,6 +12,10 @@
 #include <boost/fusion/iterator/deref.hpp>
 #include <boost/fusion/algorithm/transformation/transform.hpp>
 #include <boost/fusion/sequence/conversion/as_vector.hpp>
+#include <boost/fusion/support/unused.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
 
 namespace boost { namespace fusion {
 
@@ -23,7 +27,9 @@ namespace boost { namespace fusion {
         {
             template<typename It>
             struct result
-                : result_of::deref<It>
+                : mpl::eval_if<is_same<It, unused_type>,
+                               mpl::identity<unused_type>,
+                               result_of::deref<It> >
             {};
 
             template<typename It>
@@ -32,6 +38,11 @@ namespace boost { namespace fusion {
             {
                 return fusion::deref(it);
             }
+
+            unused_type operator()(unused_type const&) const
+            {
+                return unused_type();
+            }
         };
     }
 
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/end_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/end_impl.hpp
index 40c05f89..9f4b66cc 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/end_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/end_impl.hpp
@@ -20,21 +20,34 @@
 #include <boost/mpl/assert.hpp>
 #include <boost/mpl/min.hpp>
 
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
+
 namespace boost { namespace fusion {
 
     struct zip_view_tag;
 
     namespace detail
     {
+        template<typename SeqRef, typename M>
+        struct get_endpoint
+        {
+            typedef typename remove_reference<SeqRef>::type Seq;
+            typedef typename result_of::begin<Seq>::type begin;
+            typedef typename result_of::advance<begin, M>::type type;            
+        };
+
         template<typename M>
         struct endpoints
         {
             template<typename SeqRef>
             struct result
+                : mpl::eval_if<is_same<SeqRef, unused_type const&>,
+                               mpl::identity<unused_type>,
+                               get_endpoint<SeqRef, M> >
             {
-                typedef typename remove_reference<SeqRef>::type Seq;
-                typedef typename result_of::begin<Seq>::type begin;
-                typedef typename result_of::advance<begin, M>::type type;
+                BOOST_MPL_ASSERT((is_reference<SeqRef>));
             };
 
             template<typename Seq>
@@ -50,6 +63,11 @@ namespace boost { namespace fusion {
             {
                 return fusion::advance<M>(fusion::begin(seq));
             }
+
+            unused_type operator()(unused_type const&) const
+            {
+                return unused_type();
+            }
         };
     }
 
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/next_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/next_impl.hpp
index b2fb781f..b5b6e60d 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/next_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/next_impl.hpp
@@ -11,6 +11,10 @@
 #include <boost/fusion/sequence/view/zip_view/zip_view_iterator_fwd.hpp>
 #include <boost/fusion/iterator/next.hpp>
 #include <boost/fusion/algorithm/transformation/transform.hpp>
+#include <boost/fusion/support/unused.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
 
 namespace boost { namespace fusion {
 
@@ -22,7 +26,9 @@ namespace boost { namespace fusion {
         {
             template<typename It>
             struct result
-                : result_of::next<It>
+                : mpl::eval_if<is_same<It, unused_type>,
+                               mpl::identity<unused_type>,
+                               result_of::next<It> >
             {};
 
             template<typename It>
@@ -31,6 +37,11 @@ namespace boost { namespace fusion {
             {
                 return fusion::next(it);
             }
+
+            unused_type operator()(unused_type const&) const
+            {
+                return unused_type();
+            }
         };
     }
 
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/prior_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/prior_impl.hpp
index 9c8b8146..c174e0cc 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/prior_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/prior_impl.hpp
@@ -11,6 +11,10 @@
 #include <boost/fusion/sequence/view/zip_view/zip_view_iterator_fwd.hpp>
 #include <boost/fusion/iterator/prior.hpp>
 #include <boost/fusion/algorithm/transformation/transform.hpp>
+#include <boost/fusion/support/unused.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
 
 namespace boost { namespace fusion {
 
@@ -22,7 +26,9 @@ namespace boost { namespace fusion {
         {
             template<typename It>
             struct result
-                : result_of::prior<It>
+                : mpl::eval_if<is_same<It, unused_type>,
+                               mpl::identity<unused_type>,
+                               result_of::prior<It> >
             {};
 
             template<typename It>
@@ -31,6 +37,11 @@ namespace boost { namespace fusion {
             {
                 return fusion::prior(it);
             }
+
+            unused_type operator()(unused_type const&) const
+            {
+                return unused_type();
+            }
         };
     }
 
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/value_at_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/value_at_impl.hpp
index d0f2f44d..1fb298ec 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/value_at_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/value_at_impl.hpp
@@ -12,6 +12,10 @@
 #include <boost/fusion/algorithm/transformation/transform.hpp>
 #include <boost/fusion/sequence/intrinsic/value_at.hpp>
 #include <boost/type_traits/remove_reference.hpp>
+#include <boost/fusion/support/unused.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
 
 namespace boost { namespace fusion {
     
@@ -24,7 +28,9 @@ namespace boost { namespace fusion {
         {
             template<typename Seq>
             struct result
-                : result_of::value_at<typename remove_reference<Seq>::type, N>
+                : mpl::eval_if<is_same<Seq, unused_type const&>,
+                               mpl::identity<unused_type>,
+                               result_of::value_at<typename remove_reference<Seq>::type, N> >
             {};
         };
     }
diff --git a/include/boost/fusion/sequence/view/zip_view/detail/value_of_impl.hpp b/include/boost/fusion/sequence/view/zip_view/detail/value_of_impl.hpp
index 7f55d8fa..e8237ec1 100644
--- a/include/boost/fusion/sequence/view/zip_view/detail/value_of_impl.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/detail/value_of_impl.hpp
@@ -12,6 +12,10 @@
 #include <boost/fusion/algorithm/transformation/transform.hpp>
 #include <boost/fusion/iterator/value_of.hpp>
 #include <boost/mpl/placeholders.hpp>
+#include <boost/fusion/support/unused.hpp>
+#include <boost/mpl/eval_if.hpp>
+#include <boost/mpl/identity.hpp>
+#include <boost/type_traits/is_same.hpp>
 
 namespace boost { namespace fusion {
 
@@ -23,7 +27,9 @@ namespace boost { namespace fusion {
         {
             template<typename It>
             struct result
-                : result_of::value_of<It>
+                : mpl::eval_if<is_same<It, unused_type>,
+                               mpl::identity<unused_type>,
+                               result_of::value_of<It> >
             {};
         };
     }
diff --git a/include/boost/fusion/sequence/view/zip_view/zip_view.hpp b/include/boost/fusion/sequence/view/zip_view/zip_view.hpp
index 2d1892b1..f3bc5cd9 100644
--- a/include/boost/fusion/sequence/view/zip_view/zip_view.hpp
+++ b/include/boost/fusion/sequence/view/zip_view/zip_view.hpp
@@ -9,6 +9,7 @@
 #define FUSION_ZIP_VIEW_23012006_0813
 
 #include <boost/fusion/support/sequence_base.hpp>
+#include <boost/fusion/support/unused.hpp>
 #include <boost/fusion/iterator/equal_to.hpp>
 #include <boost/fusion/sequence/view/zip_view/detail/strictest_traversal.hpp>
 #include <boost/fusion/sequence/view/zip_view/detail/begin_impl.hpp>
@@ -21,6 +22,7 @@
 #include <boost/fusion/sequence/intrinsic/end.hpp>
 #include <boost/fusion/sequence/intrinsic/size.hpp>
 #include <boost/fusion/sequence/intrinsic/mpl.hpp>
+#include <boost/fusion/algorithm/transformation/remove.hpp>
 
 #include <boost/mpl/assert.hpp>
 #include <boost/mpl/not.hpp>
@@ -73,13 +75,14 @@ namespace boost { namespace fusion {
     template<typename Sequences>
     struct zip_view : sequence_base< zip_view<Sequences> >
     {
+        typedef typename result_of::remove<Sequences, unused_type const&>::type real_sequences;
         BOOST_MPL_ASSERT((detail::all_references<Sequences>));
-        typedef typename detail::strictest_traversal<Sequences>::type category;
+        typedef typename detail::strictest_traversal<real_sequences>::type category;
         typedef zip_view_tag fusion_tag;
         typedef fusion_sequence_tag tag; // this gets picked up by MPL
         typedef mpl::true_ is_view;
         typedef typename fusion::result_of::as_vector<Sequences>::type sequences;
-        typedef typename detail::min_size<Sequences>::type size;
+        typedef typename detail::min_size<real_sequences>::type size;
 
         zip_view(
             const Sequences& seqs)
diff --git a/include/boost/fusion/support.hpp b/include/boost/fusion/support.hpp
index ba652d7d..012ee107 100644
--- a/include/boost/fusion/support.hpp
+++ b/include/boost/fusion/support.hpp
@@ -17,5 +17,6 @@
 #include <boost/fusion/support/tag_of.hpp>
 #include <boost/fusion/support/deduce.hpp>
 #include <boost/fusion/support/deduce_sequence.hpp>
+#include <boost/fusion/support/unused.hpp>
 
 #endif
diff --git a/include/boost/fusion/support/unused.hpp b/include/boost/fusion/support/unused.hpp
new file mode 100644
index 00000000..dc2014ec
--- /dev/null
+++ b/include/boost/fusion/support/unused.hpp
@@ -0,0 +1,62 @@
+/*=============================================================================
+    Copyright (c) 2001-2006 Joel de Guzman
+
+    Distributed under the Boost Software License, Version 1.0. (See accompanying 
+    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+==============================================================================*/
+#if !defined(BOOST_FUSION_SUPPORT_UNUSED_20070305_1038)
+#define BOOST_FUSION_SUPPORT_UNUSED_20070305_1038
+
+#include <boost/config.hpp>
+#if defined(BOOST_MSVC)
+# pragma warning(push)
+# pragma warning(disable: 4522) // multiple assignment operators specified warning
+#endif
+
+namespace boost { namespace fusion {
+    struct unused_type
+    {
+        unused_type()
+        {
+        }
+
+        template <typename T>
+        unused_type(T const&)
+        {
+        }
+
+        template <typename T>
+        unused_type const&
+        operator=(T const&) const
+        {
+            return *this;
+        }
+
+        template <typename T>
+        unused_type&
+        operator=(T const&)
+        {
+            return *this;
+        }
+
+        unused_type const&
+        operator=(unused_type const&) const
+        {
+            return *this;
+        }
+
+        unused_type&
+        operator=(unused_type const&)
+        {
+            return *this;
+        }
+    };
+
+    unused_type const unused = unused_type();
+}}
+
+#if defined(BOOST_MSVC)
+# pragma warning(pop)
+#endif
+
+#endif