#973: implement default proxy

examples/callback/callback_context.cc

@@ -96,6 +96,38 @@ static void handler(CallbackMsg* msg) {
 // Some instance of the context
 static MyContext my_global_ctx = {};
 
+namespace {
+
+struct DefaultProxyElem {
+  explicit DefaultProxyElem(vt::NodeType in_node) : node_(in_node) {}
+
+  template <typename MsgT, vt::ActiveTypedFnType<MsgT>* fn, typename... Args>
+  void send(Args&&... args) const {
+    vt::theMsg()->sendMsg<MsgT, fn>(
+      node_, vt::makeMessage<MsgT>(std::forward<Args>(args)...)
+    );
+  }
+
+  private:
+  vt::NodeType node_;
+};
+
+struct DefaultProxy {
+  DefaultProxyElem operator[](vt::NodeType node) const {
+    return DefaultProxyElem{node};
+  }
+
+  static const DefaultProxy& get() {
+    static DefaultProxy const default_proxy;
+    return default_proxy;
+  }
+
+  private:
+  DefaultProxy() = default;
+};
+
+}
+
 int main(int argc, char** argv) {
   vt::initialize(argc, argv);
 
@@ -108,8 +140,9 @@ int main(int argc, char** argv) {
     auto cb = vt::theCB()->makeFunc<DataMsg,MyContext>(
       vt::pipe::LifetimeEnum::Once, &my_global_ctx, callbackFn
     );
-    auto msg = vt::makeMessage<CallbackMsg>(cb);
-    vt::theMsg()->sendMsg<CallbackMsg,handler>(1, msg);
+
+    auto const& default_proxy = DefaultProxy::get();
+    default_proxy[1].send<CallbackMsg, handler>(cb);
   }
 
   vt::finalize();