Template visitor pattern for Handlers.

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

3 files changed, 133 insertions, 0 deletions

diff --git a/cpp/src/qpid/framing/Visitor.h b/cpp/src/qpid/framing/Visitor.h
new file mode 100644
index 0000000000..fd55c48c60
--- /dev/null
+++ b/cpp/src/qpid/framing/Visitor.h
@@ -0,0 +1,71 @@
+#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*/
diff --git a/cpp/src/tests/Makefile.am b/cpp/src/tests/Makefile.am
index edb4f5b375..82918c1aec 100644
--- a/cpp/src/tests/Makefile.am
+++ b/cpp/src/tests/Makefile.am
@@ -50,6 +50,10 @@ check_PROGRAMS+=Serializer
 Serializer_SOURCES=Serializer.cpp
 Serializer_LDADD=-lboost_unit_test_framework $(lib_common)
 
+check_PROGRAMS+=Visitor
+Visitor_SOURCES=Visitor.cpp
+Visitor_LDADD=-lboost_unit_test_framework
+
 include cluster.mk
 
 # NB: CppUnit test libraries below will be migrated to boost test programs.
diff --git a/cpp/src/tests/Visitor.cpp b/cpp/src/tests/Visitor.cpp
new file mode 100644
index 0000000000..f491624cf8
--- /dev/null
+++ b/cpp/src/tests/Visitor.cpp
@@ -0,0 +1,58 @@
+/*
+ *
+ * Copyright (c) 2006 The Apache Software Foundation
+ *
+ * Licensed 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 "qpid/framing/Visitor.h"
+
+#define BOOST_AUTO_TEST_MAIN    // Must come before #include<boost/test/*>
+#include <boost/test/auto_unit_test.hpp>
+#include <boost/tuple/tuple.hpp>
+
+using namespace std;
+using namespace qpid::framing;
+
+struct DummyA;
+struct DummyB;
+struct DummyC;
+
+typedef HandlerVisitor<boost::mpl::vector<DummyA&, DummyB&, DummyC&> > DummyVisitor;
+
+struct DummyFrame : public AbstractVisitable<DummyVisitor> {};
+
+struct DummyA : public ConcreteVisitable<DummyA&, DummyFrame> {};
+struct DummyB : public ConcreteVisitable<DummyB&, DummyFrame> {};
+struct DummyC : public ConcreteVisitable<DummyC&, DummyFrame> {};
+
+struct TestDummyVisitor : public DummyVisitor {
+    boost::tuple<DummyA*, DummyB*, DummyC*> dummies;
+    void handle(DummyA& a) { dummies.get<0>() = &a; }
+    void handle(DummyB& b) { dummies.get<1>() = &b; }
+    void handle(DummyC& c) { dummies.get<2>() = &c; }
+};
+
+BOOST_AUTO_TEST_CASE(Visitor_accept) {
+    TestDummyVisitor v;
+    DummyA a;
+    DummyB b;
+    DummyC c;
+    a.accept(v);
+    BOOST_CHECK_EQUAL(&a, v.dummies.get<0>());
+    b.accept(v);
+    BOOST_CHECK_EQUAL(&b, v.dummies.get<1>());
+    c.accept(v);
+    BOOST_CHECK_EQUAL(&c, v.dummies.get<2>());
+}