Use std::unique_ptr for CZMQNotifierFactory.

Instead of returning a raw pointer from CZMQNotifierFactory and
implicitly requiring the caller to know that it has to take ownership,
return a std::unique_ptr to make this explicit.

This also changes the typedef for CZMQNotifierFactory to use the new
C++11 using syntax, which makes it (a little) less cryptic.

src/zmq/zmqabstractnotifier.h

@@ -7,10 +7,14 @@
 
 #include <zmq/zmqconfig.h>
 
+#include <util/memory.h>
+
+#include <memory>
+
 class CBlockIndex;
 class CZMQAbstractNotifier;
 
-typedef CZMQAbstractNotifier* (*CZMQNotifierFactory)();
+using CZMQNotifierFactory = std::unique_ptr<CZMQAbstractNotifier> (*)();
 
 class CZMQAbstractNotifier
 {
@@ -21,9 +25,9 @@ public:
     virtual ~CZMQAbstractNotifier();
 
     template <typename T>
-    static CZMQAbstractNotifier* Create()
+    static std::unique_ptr<CZMQAbstractNotifier> Create()
     {
-        return new T();
+        return MakeUnique<T>();
     }
 
     std::string GetType() const { return type; }

src/zmq/zmqnotificationinterface.cpp

@@ -45,13 +45,13 @@ CZMQNotificationInterface* CZMQNotificationInterface::Create()
         std::string arg("-zmq" + entry.first);
         if (gArgs.IsArgSet(arg))
         {
-            CZMQNotifierFactory factory = entry.second;
-            std::string address = gArgs.GetArg(arg, "");
-            CZMQAbstractNotifier *notifier = factory();
+            const auto& factory = entry.second;
+            const std::string address = gArgs.GetArg(arg, "");
+            std::unique_ptr<CZMQAbstractNotifier> notifier = factory();
             notifier->SetType(entry.first);
             notifier->SetAddress(address);
             notifier->SetOutboundMessageHighWaterMark(static_cast<int>(gArgs.GetArg(arg + "hwm", CZMQAbstractNotifier::DEFAULT_ZMQ_SNDHWM)));
-            notifiers.emplace_back(notifier);
+            notifiers.push_back(std::move(notifier));
         }
     }