Single, Completable, and Maybe

There are a few specialized flavors of Observable that are explicitly set up for one or no emissions: Single, Maybe, and Completable. They all follow Observable closely and should be intuitive to use in your reactive coding workflow.

You can create them in similar ways as the Observable (for example, they each have their own create() factory), but certain Observable operators may return them too.

Single

The Single<T> class is essentially an Observable<T> that emits only one item and, as such, is limited only to operators that make sense for a single emission. Similar to the Observable class (which implements ObservableSource), the Single class implements the SingleSource functional...