Template visitors for amqp_0_10::Command, Control and Struct.

Serialization for all str/vbin types.


git-svn-id: https://svn.apache.org/repos/asf/incubator/qpid/trunk/qpid@632457 13f79535-47bb-0310-9956-ffa450edef68

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+#ifndef QPID_AMQP_0_10_APPLY_H
+#define QPID_AMQP_0_10_APPLY_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 <boost/optional.hpp>
+
+namespace qpid {
+namespace amqp_0_10 {
+
+template <class F, class R=typename F::result_type> struct FunctionAndResult {
+    F* functor;
+    boost::optional<R> result;
+
+    FunctionAndResult() : functor(0) {}
+    template <class T> void invoke(T t) { result=(*functor)(t); }
+    R getResult() { return *result; }
+};
+
+// void result is special case.
+template <class F> struct FunctionAndResult<F, void> {
+    F* functor;
+    
+    FunctionAndResult() : functor(0) {}
+    template <class T> void invoke(T t) { (*functor)(t); }
+    void getResult() {}
+};
+
+template <class V, class F>
+struct ApplyVisitorBase : public V, public FunctionAndResult<F> {
+    using V::visit;
+};
+
+// Specialize for each visitor type
+template <class V, class F> struct ApplyVisitor;
+
+/** Apply a functor to a visitable object.
+ * The functor can have operator() overloads for each visitable type
+ * and/or templated operator().
+ */
+template <class F, class Visitable>
+typename F::result_type apply(F& functor, Visitable& visitable) {
+    ApplyVisitor<typename Visitable::Visitor, F> visitor;
+    visitor.functor=&functor;
+    visitable.accept(visitor);
+    return visitor.getResult();
+}
+
+template <class F, class Visitable>
+typename F::result_type apply(const F& functor, Visitable& visitable) {
+    ApplyVisitor<typename Visitable::Visitor, const F> visitor;
+    visitor.functor=&functor;
+    visitable.accept(visitor);
+    return visitor.getResult();
+}
+
+}} // namespace qpid::amqp_0_10
+
+#endif  /*!QPID_AMQP_0_10_APPLY_H*/