fun printString(string: String) = println(string)

/**
 * Prints successfully
 */
Observable.just("Test string")
    .doOnNext{ printString(it) }
    .subscribe()

/**
 * Prints successfully
 */
Observable.just("Test string")
    .doOnNext(this::printString)
    .subscribe()

/**
 * Does not print
 */
Observable.just("Test string")
    .doOnNext { this::printString }
    .subscribe()