#include <QCoreApplication>
#include <QPromise>
#include <QFuture>
#include <QDebug>

int main(int argc, char *argv[])
{
    QCoreApplication app(argc, argv);

    QObject *context = new QObject;

    QPromise<int> p;
    QFuture<int> f = p.future();

    f.then(context, [](int a) {
        qDebug("result is %d", a); // this is never called
    });

    p.start();
    p.addResult(43);
    p.finish(); // this never returns

    return app.exec();
}