Template visitor pattern for Handlers.

git-svn-id: https://svn.apache.org/repos/asf/incubator/qpid/trunk/qpid@561128 13f79535-47bb-0310-9956-ffa450edef68

1 files changed, 71 insertions, 0 deletions

diff --git a/cpp/src/qpid/framing/Visitor.h b/cpp/src/qpid/framing/Visitor.h
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+#ifndef QPID_FRAMING_VISITOR_H
+#define QPID_FRAMING_VISITOR_H
+
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ *
+ */
+
+#include "Handler.h"
+
+#include <boost/mpl/vector.hpp>
+#include <boost/mpl/inherit.hpp>
+#include <boost/mpl/inherit_linearly.hpp>
+#include <boost/type_traits/add_reference.hpp>
+
+namespace qpid {
+namespace framing {
+
+// FIXME aconway 2007-07-30: Drop linking from handlers, use
+// vector<shared_ptr<Handler<T> > for chains.
+
+/** @file Visitor pattern for Handlers. */
+
+/**
+ * Interface for a handler visitor, inherits Handler<T> for each T in Types
+ *@param Types A boost::mpl type sequence, e.g. boost::mpl::vector.
+ */
+template <class Types>
+struct HandlerVisitor : public boost::mpl::inherit_linearly<
+    Types, boost::mpl::inherit<boost::mpl::_1, Handler<boost::mpl::_2> >
+    >::type
+{};
+
+/** Base class for hierarchy of objects visitable by Visitor */
+template <class Visitor>
+struct AbstractVisitable {
+    virtual ~AbstractVisitable() {}
+    typedef Visitor VisitorType;
+    virtual void accept(Visitor& v) = 0;
+};
+
+/** Base class for concrete visitable types, implements accept.
+ * @param T parameter type for appropriate Handler, may be a reference.
+ * @param Base base class to inherit from.
+ */
+template <class T, class Base>
+struct ConcreteVisitable : public Base {
+    typedef typename boost::add_reference<T>::type TRef;
+    void accept(typename Base::VisitorType& v) {
+        static_cast<Handler<T>& >(v).handle(static_cast<TRef>(*this));
+    }
+};
+
+}} // namespace qpid::framing
+
+#endif  /*!QPID_FRAMING_VISITOR_H*/