2.x: Convert Observable to Single without a default value

[vanniktech]

With the RC3 changes I don't see an easy way of converting an Observable into a Single without giving a default value.

How do you feel about adding methods for that?

[akarnokd]

@abersnaze didn't like throwing because being empty. Try your API through Maybe and switchIfEmpty(Maybe.error()).

Edit wrong method name, fixed.

[vanniktech]

defaultIfEmpty(MaybeSource<T>) does not exist

[akarnokd]

Yeah sorry, switchIfEmpty() (I sometimes mix the two as defaultIfEmpty delegates to switchIfEmpty).

[vanniktech]

I don't quite see how switchIfEmpty solves my original problem. Maybe.switchIfEmpty() still returns a Maybe.

Also I'd rather have a NoSuchElementException and fail early than passing in a default value when converting an Observable to Single.

[akarnokd]

You could restore toSingle (under singleOrError), only the surface API has been removed.

[vanniktech]

So basically add to Observable + Flowable:

singleOrError
firstOrError
lastOrError
elementAtOrError

[akarnokd]

Yes.

[vanniktech]

Alright cool will do

[abersnaze]

Does singleElement() error on more than one but not on empty?

[akarnokd]

Yes, that was kept and also why firstElement is there to ignore more without signalling.

[JakeWharton]

This can be closed right?