RxKotlin is a lightweight library that adds convenient extension functions to RxJava. You can use RxJava with Kotlin out-of-the-box, but Kotlin has language features (such as extension functions) that can streamline usage of RxJava even more. RxKotlin aims to conservatively collect these conveniences in one centralized library, and standardize conventions for using RxJava with Kotlin.

import io.reactivex.rxjava3.kotlin.subscribeBy
import io.reactivex.rxjava3.kotlin.toObservable

fun main(args: Array<String>) {

    val list = listOf("Alpha", "Beta", "Gamma", "Delta", "Epsilon")

    list.toObservable() // extension function for Iterables
            .filter { it.length >= 5 }
            .subscribeBy(  // named arguments for lambda Subscribers
                    onNext = { println(it) },
                    onError =  { it.printStackTrace() },
                    onComplete = { println("Done!") }
            )

}

Since Kotlin makes it easy to implement extensions for anything and everything, this project has to be conservative in what features are in scope. Intentions to create syntactic sugar can quickly regress into syntactic saccharin, and such personal preferences belong in one's internal domain rather than an OSS library.

Here are some basic guidelines to determine whether your contribution might be in scope for RxKotlin:

• Is this intended feature already in RxJava?

  • If no, propose the operator in RxJava.
  • If yes, can Kotlin streamline the operator further?

• Does this substantially reduce the amount of boilerplate code?

• Does this make an existing operator easier to use?

• Does RxJava not contain this feature due to Java language limitations, or because of a deliberate decision to not include it?

Join us on the #rx channel in Kotlin Slack!

https://kotlinlang.slack.com/messages/rx

Use RxKotlin 3.x versions to target RxJava 3.x.

• The 3.x version is active.

Use RxKotlin 2.x versions to target RxJava 2.x.

• The 2.x version of RxJava and RxKotlin is in maintenance mode and will be supported only through bugfixes. No new features or behavior changes will be accepted or applied.

Use RxKotlin 1.x versions to target RxJava 1.x.

• The 1.x version of RxJava and RxKotlin reached end-of-life. No further development, support, maintenance, PRs or updates will happen.

The maintainers do not update the RxJava dependency version for every minor or patch RxJava release, so you should explicitly add the desired RxJava dependency version to your pom.xml or build.gradle(.kts).

Binaries and dependency information for Maven, Ivy, Gradle and others can be found at https://search.maven.org.

Example for Maven:

<dependency>
    <groupId>io.reactivex.rxjava3</groupId>
    <artifactId>rxkotlin</artifactId>
    <version>3.x.y</version>
</dependency>

Example for Gradle:

implementation("io.reactivex.rxjava3:rxkotlin:3.x.y")

Example for Maven:

<dependency>
    <groupId>io.reactivex.rxjava2</groupId>
    <artifactId>rxkotlin</artifactId>
    <version>2.x.y</version>
</dependency>

Example for Gradle:

implementation("io.reactivex.rxjava2:rxkotlin:2.x.y")

Example for Maven:

<dependency>
    <groupId>io.reactivex</groupId>
    <artifactId>rxkotlin</artifactId>
    <version>1.x.y</version>
</dependency>

Example for Gradle:

implementation("io.reactivex:rxkotlin:1.x.y")

You can also use Gradle or Maven with JitPack to build directly off a snapshot, branch, or commit of this repository.

For example, to build off the 3.x branch, use this setup for Gradle:

repositories {
    maven { url 'https://jitpack.io' }
}

dependencies {
    implementation 'com.github.ReactiveX:RxKotlin:3.x-SNAPSHOT'
}

Use this setup for Maven:

	<repositories>
		<repository>
		    <id>jitpack.io</id>
		    <url>https://jitpack.io</url>
		</repository>
	</repositories>

    <dependency>
	    <groupId>com.github.ReactiveX</groupId>
	    <artifactId>RxKotlin</artifactId>
	    <version>3.x-SNAPSHOT</version>
	</dependency>

Learn more about building this project with JitPack here.

To help cope with the SAM ambiguity issue when using RxJava with Kotlin, there are a number of helper factories and extension functions to workaround the affected operators.

Observables.zip()
Observables.combineLatest()
Observable#zipWith()
Observable#withLatestFrom()
Flowables.zip()
Flowables.combineLatest()
Flowable#zipWith()
Flowable#withLatestFrom()
Singles.zip()
Single#zipWith()
Maybes.zip()

RxKotlin can be used in conjunction with other Rx and Kotlin libraries, such as RxAndroid, RxBinding, and TornadoFX/RxKotlinFX. These libraries and RxKotlin are modular, and RxKotlin is merely a set of extension functions to RxJava that can be used with these other libraries. There should be no overlap or dependency issues.

Chapter 12 of Learning RxJava covers RxKotlin and Kotlin idioms with RxJava.

The book Reactive Programming in Kotlin mainly focuses on RxKotlin, as well as learning reactive programming with Kotlin.