整理

include/boost/mpl/aux_/erase_impl.hpp

@@ -0,0 +1,69 @@
+
+#ifndef BOOST_MPL_AUX_ERASE_IMPL_HPP_INCLUDED
+#define BOOST_MPL_AUX_ERASE_IMPL_HPP_INCLUDED
+
+// Copyright Aleksey Gurtovoy 2000-2004
+//
+// 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)
+//
+// See http://www.boost.org/libs/mpl for documentation.
+
+// $Id$
+// $Date$
+// $Revision$
+
+#include <boost/mpl/clear.hpp>
+#include <boost/mpl/push_front.hpp>
+#include <boost/mpl/reverse_fold.hpp>
+#include <boost/mpl/iterator_range.hpp>
+#include <boost/mpl/next.hpp>
+#include <boost/mpl/aux_/na.hpp>
+
+namespace boost { namespace mpl {
+
+// default implementation; conrete sequences might override it by 
+// specializing either the 'erase_impl' or the primary 'erase' template
+
+template< typename Tag >
+struct erase_impl
+{
+    template<
+          typename Sequence
+        , typename First
+        , typename Last
+        >
+    struct apply
+    {
+        typedef typename if_na< Last,typename next<First>::type >::type last_;
+        
+        // 1st half: [begin, first)
+        typedef iterator_range<
+              typename begin<Sequence>::type
+            , First
+            > first_half_;
+
+        // 2nd half: [last, end) ... that is, [last + 1, end)
+        typedef iterator_range<
+              last_
+            , typename end<Sequence>::type
+            > second_half_;
+
+        typedef typename reverse_fold<
+              second_half_
+            , typename clear<Sequence>::type
+            , push_front<_,_>
+            >::type half_sequence_;
+
+        typedef typename reverse_fold<
+              first_half_
+            , half_sequence_
+            , push_front<_,_>
+            >::type type;
+    };
+};
+
+}}
+
+#endif // BOOST_MPL_AUX_ERASE_IMPL_HPP_INCLUDED