Redesign inheritance from Message (#62)

... so that the code is more idiomatic, clear and expressive about its intended use

src/Connection.cpp

@@ -25,6 +25,7 @@
 
 #include "Connection.h"
 #include "SdBus.h"
+#include "MessageUtils.h"
 #include <sdbus-c++/Message.h>
 #include <sdbus-c++/Error.h>
 #include "ScopeGuard.h"
@@ -169,7 +170,7 @@ MethodCall Connection::createMethodCall( const std::string& destination
 
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to create method call", -r);
 
-    return MethodCall{sdbusMsg, iface_.get(), adopt_message};
+    return Message::Factory::create<MethodCall>(sdbusMsg, iface_.get(), adopt_message);
 }
 
 Signal Connection::createSignal( const std::string& objectPath
@@ -186,7 +187,7 @@ Signal Connection::createSignal( const std::string& objectPath
 
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to create signal", -r);
 
-    return Signal{sdbusSignal, iface_.get(), adopt_message};
+    return Message::Factory::create<Signal>(sdbusSignal, iface_.get(), adopt_message);
 }
 
 void Connection::emitPropertiesChangedSignal( const std::string& objectPath

src/Message.cpp

@@ -639,7 +639,7 @@ MethodReply MethodCall::sendWithReply() const
 
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to call method", -r);
 
-    return MethodReply{sdbusReply, sdbus_, adopt_message};
+    return Factory::create<MethodReply>(sdbusReply, sdbus_, adopt_message);
 }
 
 MethodReply MethodCall::sendWithNoReply() const
@@ -647,7 +647,7 @@ MethodReply MethodCall::sendWithNoReply() const
     auto r = sdbus_->sd_bus_send(nullptr, (sd_bus_message*)msg_, nullptr);
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to call method with no reply", -r);
 
-    return MethodReply{}; // No reply
+    return Factory::create<MethodReply>(); // No reply
 }
 
 MethodReply MethodCall::createReply() const
@@ -656,7 +656,7 @@ MethodReply MethodCall::createReply() const
     auto r = sdbus_->sd_bus_message_new_method_return((sd_bus_message*)msg_, &sdbusReply);
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to create method reply", -r);
 
-    return MethodReply{sdbusReply, sdbus_, adopt_message};
+    return Factory::create<MethodReply>(sdbusReply, sdbus_, adopt_message);
 }
 
 MethodReply MethodCall::createErrorReply(const Error& error) const
@@ -669,7 +669,7 @@ MethodReply MethodCall::createErrorReply(const Error& error) const
     auto r = sdbus_->sd_bus_message_new_method_error((sd_bus_message*)msg_, &sdbusErrorReply, &sdbusError);
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to create method error reply", -r);
 
-    return MethodReply{sdbusErrorReply, sdbus_, adopt_message};
+    return Factory::create<MethodReply>(sdbusErrorReply, sdbus_, adopt_message);
 }
 
 AsyncMethodCall::AsyncMethodCall(MethodCall&& call) noexcept
@@ -699,7 +699,7 @@ void Signal::send() const
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to emit signal", -r);
 }
 
-Message createPlainMessage()
+PlainMessage createPlainMessage()
 {
     int r;
 
@@ -736,7 +736,7 @@ Message createPlainMessage()
     r = sd_bus_message_new(bus, &sdbusMsg, _SD_BUS_MESSAGE_TYPE_INVALID);
     SDBUS_THROW_ERROR_IF(r < 0, "Failed to create a new message", -r);
 
-    return Message{sdbusMsg, &sdbus, adopt_message};
+    return Message::Factory::create<PlainMessage>(sdbusMsg, &sdbus, adopt_message);
 }
 
 }

src/MessageUtils.h

@@ -30,7 +30,35 @@
 
 namespace sdbus
 {
-    Message createPlainMessage();
+    class Message::Factory
+    {
+    public:
+        template<typename _Msg>
+        static _Msg create()
+        {
+            return _Msg{};
+        }
+
+        template<typename _Msg>
+        static _Msg create(void *msg)
+        {
+            return _Msg{msg};
+        }
+
+        template<typename _Msg>
+        static _Msg create(void *msg, internal::ISdBus* sdbus)
+        {
+            return _Msg{msg, sdbus};
+        }
+
+        template<typename _Msg>
+        static _Msg create(void *msg, internal::ISdBus* sdbus, adopt_message_t)
+        {
+            return _Msg{msg, sdbus, adopt_message};
+        }
+    };
+
+    PlainMessage createPlainMessage();
 }
 
 #endif /* SDBUS_CXX_INTERNAL_MESSAGEUTILS_H_ */

src/Object.cpp

@@ -24,6 +24,7 @@
  */
 
 #include "Object.h"
+#include "MessageUtils.h"
 #include <sdbus-c++/IConnection.h>
 #include <sdbus-c++/Message.h>
 #include <sdbus-c++/Error.h>
@@ -260,7 +261,7 @@ int Object::sdbus_method_callback(sd_bus_message *sdbusMessage, void *userData,
     auto* object = static_cast<Object*>(userData);
     assert(object != nullptr);
 
-    MethodCall message{sdbusMessage, &object->connection_.getSdBusInterface()};
+    auto message = Message::Factory::create<MethodCall>(sdbusMessage, &object->connection_.getSdBusInterface());
 
     // Note: The lookup can be optimized by using sorted vectors instead of associative containers
     auto& callback = object->interfaces_[message.getInterfaceName()].methods_[message.getMemberName()].callback_;
@@ -298,7 +299,7 @@ int Object::sdbus_property_get_callback( sd_bus */*bus*/
         return 1;
     }
 
-    Message reply{sdbusReply, &object->connection_.getSdBusInterface()};
+    auto reply = Message::Factory::create<PropertyGetReply>(sdbusReply, &object->connection_.getSdBusInterface());
 
     try
     {
@@ -327,7 +328,7 @@ int Object::sdbus_property_set_callback( sd_bus */*bus*/
     auto& callback = object->interfaces_[interface].properties_[property].setCallback_;
     assert(callback);
 
-    Message value{sdbusValue, &object->connection_.getSdBusInterface()};
+    auto value = Message::Factory::create<PropertySetCall>(sdbusValue, &object->connection_.getSdBusInterface());
 
     try
     {

src/Proxy.cpp

@@ -25,6 +25,7 @@
 
 #include "Proxy.h"
 #include "IConnection.h"
+#include "MessageUtils.h"
 #include "sdbus-c++/Message.h"
 #include "sdbus-c++/IConnection.h"
 #include "sdbus-c++/Error.h"
@@ -137,7 +138,7 @@ int Proxy::sdbus_async_reply_handler(sd_bus_message *sdbusMessage, void *userDat
 
     SCOPE_EXIT{ proxy.pendingAsyncCalls_.removeCall(asyncCallData->slot.get()); };
 
-    MethodReply message{sdbusMessage, &proxy.connection_->getSdBusInterface()};
+    auto message = Message::Factory::create<MethodReply>(sdbusMessage, &proxy.connection_->getSdBusInterface());
 
     const auto* error = sd_bus_message_get_error(sdbusMessage);
     if (error == nullptr)
@@ -158,7 +159,7 @@ int Proxy::sdbus_signal_callback(sd_bus_message *sdbusMessage, void *userData, s
     auto* proxy = static_cast<Proxy*>(userData);
     assert(proxy != nullptr);
 
-    Signal message{sdbusMessage, &proxy->connection_->getSdBusInterface()};
+    auto message = Message::Factory::create<Signal>(sdbusMessage, &proxy->connection_->getSdBusInterface());
 
     // Note: The lookup can be optimized by using sorted vectors instead of associative containers
     auto& callback = proxy->interfaces_[message.getInterfaceName()].signals_[message.getMemberName()].callback_;