[c++ grpc] Add helper io_manager_tag::tag

This function encapsulates the `static_cast<io_manager*>(thing)` pattern
that was used throughout the codebase.

cpp/inc/bond/ext/grpc/detail/client_call_data.h

@@ -72,14 +72,14 @@ struct client_unary_call_data
           _ioManager(std::move(ioManager)),
           _threadPool(std::move(threadPool)),
           _responseReader(),
-          _callbackArgs(context),
-          _cb(cb),
+          _callbackArgs(std::move(context)),
+          _cb(std::move(cb)),
           _self()
     {
         BOOST_ASSERT(_channel);
         BOOST_ASSERT(_ioManager);
         BOOST_ASSERT(_threadPool);
-        BOOST_ASSERT(context);
+        BOOST_ASSERT(_callbackArgs.context);
     }
 
     /// @brief Initiates the client request and wires up completion
@@ -88,7 +88,7 @@ struct client_unary_call_data
         const grpc::internal::RpcMethod& method,
         const bond::bonded<TRequest>& request)
     {
-        _responseReader = std::unique_ptr<grpc::ClientAsyncResponseReader<bond::bonded<TResponse>>>(
+        _responseReader.reset(
             ::grpc::internal::ClientAsyncResponseReaderFactory<bond::bonded<TResponse>>::Create(
                 _channel.get(),
                 _ioManager->cq(),
@@ -102,7 +102,7 @@ struct client_unary_call_data
         _responseReader->Finish(
             &_callbackArgs.response,
             &_callbackArgs.status,
-            static_cast<void*>(static_cast<io_manager_tag*>(this)));
+            tag());
     }
 
     /// @brief Invoked after the response has been received.
@@ -110,7 +110,7 @@ struct client_unary_call_data
     {
         if (ok && _cb)
         {
-            _threadPool->schedule([this]()
+            _threadPool->schedule([this]
             {
                 // pass a shared_ptr to unary_call_result, but that
                 // participates in shared ownership of the containing

cpp/inc/bond/ext/grpc/detail/io_manager_tag.h

@@ -15,13 +15,19 @@ namespace bond { namespace ext { namespace gRPC { namespace detail {
     /// operation in its implementation of \ref invoke.
     struct io_manager_tag
     {
-        virtual ~io_manager_tag() { }
+        virtual ~io_manager_tag() = default;
 
         /// @brief Called when this instance is dequeued from a completion
         /// queue.
         ///
         /// @param ok whether or not the initial operation succeeded
         virtual void invoke(bool ok) = 0;
+
+        /// @return Returns a %tag value suitable for passing to completion queue routines.
+        io_manager_tag* tag()
+        {
+            return this;
+        }
     };
 
 } } } } // namespace bond::ext::gRPC::detail

cpp/inc/bond/ext/grpc/detail/unary_call_impl.h

@@ -94,7 +94,7 @@ namespace bond { namespace ext { namespace gRPC { namespace detail {
             bool wasResponseSent = _responseSentFlag.test_and_set();
             if (!wasResponseSent)
             {
-                _responder.Finish(msg, status, static_cast<void*>(static_cast<io_manager_tag*>(this)));
+                _responder.Finish(msg, status, tag());
             }
         }
 
@@ -103,7 +103,7 @@ namespace bond { namespace ext { namespace gRPC { namespace detail {
             bool wasResponseSent = _responseSentFlag.test_and_set();
             if (!wasResponseSent)
             {
-                _responder.FinishWithError(status, static_cast<void*>(static_cast<io_manager_tag*>(this)));
+                _responder.FinishWithError(status, tag());
             }
         }
 
@@ -179,8 +179,6 @@ namespace bond { namespace ext { namespace gRPC { namespace detail {
     template <typename TRequest, typename TResponse>
     class unary_call_base
     {
-        using impl_type = unary_call_impl<TRequest, TResponse>;
-
     public:
         void swap(unary_call_base& rhs) noexcept
         {
@@ -240,6 +238,8 @@ namespace bond { namespace ext { namespace gRPC { namespace detail {
         }
 
     protected:
+        using impl_type = unary_call_impl<TRequest, TResponse>;
+
         unary_call_base() = default;
 
         explicit unary_call_base(boost::intrusive_ptr<impl_type> impl) noexcept

cpp/test/grpc/io_manager.cpp

@@ -61,7 +61,7 @@ class io_managerTests
 
         alarm_completion_tag<event> act;
         gpr_timespec deadline = gpr_time_0(GPR_CLOCK_MONOTONIC);
-        grpc::Alarm alarm(ioManager.cq(), deadline, static_cast<io_manager_tag*>(&act));
+        grpc::Alarm alarm(ioManager.cq(), deadline, act.tag());
 
         bool wasSet = act.completion_event.wait_for(std::chrono::seconds(30));
         UT_AssertIsTrue(wasSet);
@@ -81,7 +81,7 @@ class io_managerTests
         alarms.reserve(numItems);
         for (size_t i = 0; i < numItems; ++i)
         {
-            alarms.emplace_back(ioManager.cq(), deadline, static_cast<io_manager_tag*>(&act));
+            alarms.emplace_back(ioManager.cq(), deadline, act.tag());
         }
 
         bool wasSet = act.completion_event.wait_for(std::chrono::seconds(30));
@@ -146,7 +146,7 @@ class io_managerTests
 
         alarm_completion_tag<event> act;
         gpr_timespec deadline = gpr_time_0(GPR_CLOCK_MONOTONIC);
-        grpc::Alarm alarm(ioManager.cq(), deadline, static_cast<io_manager_tag*>(&act));
+        grpc::Alarm alarm(ioManager.cq(), deadline, act.tag());
 
         bool wasSet = act.completion_event.wait_for(std::chrono::milliseconds(1250));
         UT_AssertIsTrue(!wasSet);