Rewrite Java code in Kotlin using Function Reference occurs SAM types conflict

I have an example Java code using method reference that I want to rewrite to Kotlin. Java version is using method reference, solution is short and clear. But on the other hand I cannot use method reference in Kotlin. The only version that I've managed to write is one presented below. It seems like Function3 { s: String, b: Boolean, i: Int -> combine(s, b, i) } could be written in cleaner way (if possible method reference would be perfect).

I'm new to Kotlin so I'll be grateful for any clues.

Java

import io.reactivex.Observable;

public class TestJava {

    Observable<String> strings() {
        return Observable.just("test");
    }

    Observable<Boolean> booleans() {
        return Observable.just(true);
    }

    Observable<Integer> integers() {
        return Observable.just(1);
    }

    void test() {
        Observable.combineLatest(strings(), booleans(), integers(),
                this::combine);
    }

    double combine(String s, boolean b, int i) {
        return 1.0;
    }
}

Kotlin

import io.reactivex.Observable
import io.reactivex.functions.Function3

class TestKotlin {

    fun strings(): Observable<String> {
        return Observable.just("test")
    }

    fun booleans(): Observable<Boolean> {
        return Observable.just(true)
    }

    fun integers(): Observable<Int> {
        return Observable.just(1)
    }

    fun test() {
        Observable.combineLatest(strings(), booleans(), integers(),
                Function3 { s: String, b: Boolean, i: Int -> combine(s, b, i) })
    }

    fun combine(s: String, b: Boolean, i: Int): Double {
        return 1.0
    }
}

EDIT

Following method references in Kotlin gives an error.

fun test() {
    Observable.combineLatest(strings(), booleans(), integers(), this::combine)
}

fun test() {
    Observable.combineLatest(strings(), booleans(), integers(), TestKotlin::combine)
}

None of the following functions can be called with the arguments supplied: @CheckReturnValue @SchedulerSupport public final fun combineLatest(p0: ((Observer) -> Unit)!, p1: ((Observer) -> Unit)!, p2: ((Observer) -> Unit)!, p3: ((???, ???, ???) -> ???)!): Observable<(???..???)>! defined in io.reactivex.Observable @CheckReturnValue @SchedulerSupport public open fun combineLatest(p0: ObservableSource!, p1: ObservableSource!, p2: ObservableSource!, p3: io.reactivex.functions.Function3!): Observable<(???..???)>! defined in io.reactivex.Observable @CheckReturnValue @SchedulerSupport public open fun combineLatest(p0: Function!, out (???..???)>!, p1: Int, vararg p2: ObservableSource!): Observable<(???..???)>! defined in io.reactivex.Observable

EDIT 2

RxKotlin solves issue mentioned in answer.

import io.reactivex.rxkotlin.Observables

class TestKotlin {

    fun test() {
        Observables.combineLatest(strings(), booleans(), integers(), this::combine)
    }

}