Exponential backoff in Kotlin with RxJava2 - kotlin

Question

I am trying to do an exponential retry for a request, so that if the request fails (i.e. your internet is down) the app retries endlessly until it works (for the amount of time the app is in the foreground)
I tried with this solution
public class RetryWithDelay implements Function<Observable<? extends Throwable>, Observable<?>> {
private final int maxRetries;
private final int retryDelayMillis;
private int retryCount;
public RetryWithDelay(final int maxRetries, final int retryDelayMillis) {
this.maxRetries = maxRetries;
this.retryDelayMillis = retryDelayMillis;
this.retryCount = 0;
}
#Override
public Observable<?> apply(final Observable<? extends Throwable> attempts) {
return attempts
.flatMap(new Function<Throwable, Observable<?>>() {
#Override
public Observable<?> apply(final Throwable throwable) {
if (++retryCount < maxRetries) {
// When this Observable calls onNext, the original
// Observable will be retried (i.e. re-subscribed).
return Observable.timer(retryDelayMillis,
TimeUnit.MILLISECONDS);
}
// Max retries hit. Just pass the error along.
return Observable.error(throwable);
}
});
}
}
But when I try to convert this to kotlin it says Function only takes one generic parameter.

Answer 1

I copy-pasted the Java code into IntelliJ and it did half the work for me:
import java.util.concurrent.TimeUnit
import io.reactivex.functions.Function
import io.reactivex.*
class RetryWithDelay(private val maxRetries: Int, private val retryDelayMillis: Long) : Function<Observable<Throwable>, Observable<Long>> {
override fun apply(attempts: Observable<Throwable>): Observable<Long> {
return attempts
.flatMap(object : Function<Throwable, Observable<Long>> {
private var retryCount: Int = 0
override fun apply(throwable: Throwable): Observable<Long> {
return if (++retryCount < maxRetries) {
// When this Observable calls onNext, the original
// Observable will be retried (i.e. re-subscribed).
Observable.timer(retryDelayMillis,
TimeUnit.MILLISECONDS)
} else Observable.error<Long>(throwable)
// Max retries hit. Just pass the error along.
}
})
}
}
Note that the retryCount has been moved into the inner flatMap so that it is not shared between multiple Observers.