What is Qt for boost::promise<T>?

Question

I see that Qt has future class that is direct analog for boost::future but what is qt for boost::promise?

Answer 1

Constructing my own QFuture as shown in the accepted answer did not work for me. At first it seemed like it was working, but in my testing I realized it was not blocking the caller. Whoops! So I dug into the code a little further and found that QFutureInterface is what you want to use as your 'promise'. Like boost::promise, QFutureInterface is what you interact with in your worker thread, and it is a factory for QFutures.

So here's what I've been doing in Qt 4.8 (not sure if this is applicable to later versions).

QFutureInterface<QVariant> promise;
promise.reportStarted();
...
promise.reportResult(someVariant);
promise.reportFinished();

Then in the client thread, assuming you have access to the QFutureInterface 'promise'

QVariant result = promise.future().result();

The future() call is a factory method for creating a QFuture bound to your QFutureInterface. You should be able to get the QFuture and call result() on it later if you wanted.