ex.cpp

    auto future = QtConcurrent::run(doHeavyStuff);
    auto watcher = new QFutureWatcher<ResultType>(this);

    connect(watcher, &QFutureWatcher<ResultType>::finished, [future]() {
        // Do stuff here, you have the return value of doHeavyStuff in future.result()...
    });

    connect(watcher, &QFutureWatcher<ResultType>::finished,
            watcher, &QFutureWatcher<ResultType>::deleteLater);

    watcher->setFuture(future);