/// <summary>
/// Keep an <paramref name="aggregate"/> subscription latest key in all <paramref name="keySequences"/> via <paramref name="sourceFactory"/>
/// </summary>
/// <remarks>Will call <paramref name="sourceFactory"/> exactly when the <paramref name="aggregate"/> changes (as decided by <paramref name="keyComparer"/>) </remarks>
/// <returns></returns>
public static IObservable <TElement> CombineSubscriptions <TKey, TAgg, TElement>(
this Func <TAgg, IObservable <TElement> > sourceFactory,
IObservable <IObservable <TKey> > keySequences,
Func <TAgg, TKey, TAgg> aggregate,
TAgg seed = default(TAgg),
IEqualityComparer <TAgg> keyComparer = null)
{
if (keyComparer == null)
{
keyComparer = EqualityComparer <TAgg> .Default;
}
return(keySequences.AggregateLatest(aggregate, seed)
.DistinctUntilChanged(keyComparer)
.Select(sourceFactory)
.Switch()
.Publish().RefCount());
}
