private fun dummyBook() : ArrayList<Book>{
    var books = arrayListOf<Book>()
    books.add(Book("Why is the snail slow?", "Alex"))
    books.add(Book("Clean code", "David"))
    return books
}

Observable.create<Book> {
    it.onNext(Book("Why is the snail slow?", "Alex"))
}.subscribe(object : Observer<Book> {
    override fun onComplete() {
        println("onComplete")
    }

    override fun onSubscribe(d: Disposable) {
        println("onSubscribe")
    }

    override fun onNext(t: Book) {
        println("onNext: $t")
    }

    override fun onError(e: Throwable) {
        println("error: ${e.message}")
    } 
})

Single.create<Book> {
    it.onSuccess(Book("Why is the snail slow?", "Alex"))
}.subscribe(object : SingleObserver<Book> {
    override fun onSuccess(t: Book) {
        println("success: $t")
    }

    override fun onSubscribe(d: Disposable) {

    }

    override fun onError(e: Throwable) {
        println("error: ${e.message}")
    }
})

Maybe.create<Book> {
    it.onSuccess(Book("Why is the snail slow?", "Alex"))
}.subscribe(object : MaybeObserver<Book> {
    override fun onSuccess(t: Book) {
        println("success: $t")
    }

    override fun onComplete() {
        println("onComplete")
    }

    override fun onSubscribe(d: Disposable) {
        println("onSubscribe")
    }

    override fun onError(e: Throwable) {
        println("error: ${e.message}")
    }

})

Completable.create {
    it.onComplete()
}.subscribe(object : CompletableObserver{
    override fun onComplete() {
        println("onComplete")
    }

    override fun onSubscribe(d: Disposable) {
        println("onSubscribe")
    }

    override fun onError(e: Throwable) {
        println("onError: ${e.message}")
    }

})