Possible to turn callback calls into IEnumerable

Question

I'm writing a wrapper around a 3rd party library, and it has a method to scan the data it manages. The method takes a callback method that it calls for each item in the data that it finds.

e.g. The method is essentially: void Scan(Action<object> callback);

I want to wrap it and expose a method like IEnumerable<object> Scan();

Is this possible without resorting to a separate thread to do the actual scan and a buffer?

Answer 1

You can do this quite simply with Reactive:

class Program
{
    static void Main(string[] args)
    {
        foreach (var x in CallBackToEnumerable<int>(Scan))
            Console.WriteLine(x);
    }

    static IEnumerable<T> CallBackToEnumerable<T>(Action<Action<T>> functionReceivingCallback)
    {
        return Observable.Create<T>(o =>
        {
            // Schedule this onto another thread, otherwise it will block:
            Scheduler.Later.Schedule(() =>
            {
                functionReceivingCallback(o.OnNext);
                o.OnCompleted();
            });

            return () => { };
        }).ToEnumerable();
    }

    public static void Scan(Action<int> act)
    {
        for (int i = 0; i < 100; i++)
        {
            // Delay to prove this is working asynchronously.
            Thread.Sleep(100);
            act(i);
        }
    }
}

Remember that this doesn't take care of things like cancellation, since the callback method doesn't really allow it. A proper solution would require work on the part of the external library.