Subscribing to an observable that is function of another observable

[martinrhan]

I have an IObservable<TypeA> instance. There is a function public static IObservable<TypeB> MyFunction(TypeA a).Now I want to subscribe to the IObservable<TypeB> object returned from MyFunction(currentTypeAObject), but when the IObservable<TypeA> has a change, the previous subscription of the TypeB object is disposed and a new subscription to whats returned by MyFunction(newTypeAObject) is established.

Whats decribed above is actually a generalization of a common scenario in UI development, that is, subscribing to a nested property, for example, given objectA, subscribe objectA.TypeAPropertyA.TypeBPropertyB. Existing frameworks somehow provide capability to subscribe the entire path, in which any part of the chain changes result into a notify to the subsribers and internal modifications of subscription states. However, they are limited and not generalized. For instance, ReactiveUI only support binding path that all parts are properties.

I would like to know if there is an elegant and swift solution for this, using existing classes in reactive extensions.

[fedeAlterio]

Exists an operator that does exactly what you ask: Switch.
observableA.Select(MyFunction).Switch()
Returns an IObservale<B> that produces values from the last observable returned from MyFunction. Basically every time a new element of a is produced, it unsubscribes from the previous IObservale<B> and subscribes to the new one.

this.WhenAnyValue(x => x.PropA) .Select(y => y.WhenAnyValue(z => z.PropB).Switch() you should be careful with nulls, but this is the idea