Dispose of Observable Items as they are generated

Question

I have an IObservable that generates items that are disposable, and it will generate a potentially infinite number of them over its lifetime. Because of this, I want to dispose of the last item each time a new item is generated, so the Using operator will not work for this. Is there a different Rx.NET operator that can accomplish this function?

Answer 1

Here is a DisposePrevious operator, based on a slightly modified version of Enigmativity's solution.

/// <summary>Disposes the previous element of an observable sequence. The last
/// element is disposed when the observable sequence completes.</summary>
public static IObservable<T> DisposePrevious<T>(this IObservable<T> source)
    where T : IDisposable
{
    return Observable.Using(() => new SerialDisposable(), serial =>
        source.Do(x => serial.Disposable = x));
}

The SerialDisposable class...

Represents a disposable resource whose underlying disposable resource can be replaced by another disposable resource, causing automatic disposal of the previous underlying disposable resource.

Answer 2

If you have a IObservable<IDisposable> source then do this to automatically dispose of the previous value and to clean up when the sequence ends:

IObservable<IDisposable> query =
    Observable.Create<IDisposable>(o =>
    {
        var serial = new SerialDisposable();
        return new CompositeDisposable(
            source.Do(x => serial.Disposable = x).Subscribe(o),
            serial);
    })