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+/* vim: set sw=4 sts=4 et foldmethod=syntax : */
+
+/*
+ * Copyright (c) 2008, 2009, 2010, 2011 Ciaran McCreesh
+ *
+ * This file is part of the Paludis package manager. Paludis is free software;
+ * you can redistribute it and/or modify it under the terms of the GNU General
+ * Public License version 2, as published by the Free Software Foundation.
+ *
+ * Paludis is distributed in the hope that it will be useful, but WITHOUT ANY
+ * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS
+ * FOR A PARTICULAR PURPOSE. See the GNU General Public License for more
+ * details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program; if not, write to the Free Software Foundation, Inc., 59 Temple
+ * Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef PALUDIS_GUARD_PALUDIS_UTIL_VISITOR_CAST_HH
+#define PALUDIS_GUARD_PALUDIS_UTIL_VISITOR_CAST_HH 1
+
+#include <paludis/util/visitor_cast-fwd.hh>
+#include <paludis/util/visitor.hh>
+#include <type_traits>
+
+namespace paludis
+{
+ template <typename To_, typename From_>
+ struct VisitorCaster
+ {
+ To_ * visit(To_ & t)
+ {
+ return &t;
+ }
+
+ To_ * visit(From_ &)
+ {
+ return 0;
+ }
+ };
+
+ template <typename To_, typename From_, bool ok_>
+ struct VerifyVisitorCastType
+ {
+ };
+
+ template <typename To_, typename From_>
+ struct VerifyVisitorCastType<To_, From_, true>
+ {
+ typedef int IsOK;
+ };
+
+ template <typename C_, typename T_>
+ struct CopyConst
+ {
+ typedef T_ Type;
+ };
+
+ template <typename C_, typename T_>
+ struct CopyConst<const C_, T_>
+ {
+ typedef const T_ Type;
+ };
+
+ template <typename To_, typename From_>
+ To_ * visitor_cast(From_ & from)
+ {
+ /* verify that we are attempting to visitor_cast something that
+ * could potentially be true */
+ typedef typename VerifyVisitorCastType<To_, From_, std::is_base_of<From_, To_>::value>::IsOK TypeIsOK;
+
+ VisitorCaster<To_, typename CopyConst<From_, typename From_::VisitableBaseClass>::Type> q;
+ return from.template accept_returning<To_ *>(q);
+ }
+}
+
+#endif