Replacing Rx operators using Kotlin operators

Well in our Android Application we have n number of network calls and many developers used “Reactive Programming(RxJava/RxAndroid)” for Api calls. But thanks to Kotlin which has provided same set of operators . Why Rx now?? Let’s see how Kotlin replace the Rx operators.

Let’s suppose I have an Api call from which I need to return list of MyGist.

val observable =  RetrofitSingleton.getInstance()!!.provideClient()
        .gistsObservable  //returning Observable
fun provideClient(){
val retrofit = Retrofit.Builder().baseUrl("https://api.github.com")
        .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
        .addConverterFactory(GsonConverterFactory.create()).build()
client = retrofit.create(GistApi::class.java)
}

val deferred = RetrofitSingleton.getInstance()!!.provideCoroutineClient()
           .gistsDeferred //returning Deferred
val listOfItems = deferred.await() // returns List<Gist>
private fun provideCoroutineClient(){
val retrofit2 = Retrofit.Builder().baseUrl("https://api.github.com")
        .addCallAdapterFactory(CoroutineCallAdapterFactory())
        .addConverterFactory(GsonConverterFactory.create()).build()
return retrofit2.create(GistApi::class.java)
}

1. Flatmap

In Rx:

observable
     .flatMap(Func1<ArrayList<Gist>, Observable<out Gist>> { Observable.from(it) })

In Kotlin:

listOfItems.flatMap { listOf(it)}  //simply converting it into list you can apply function on it

2. Filter

In Rx:

observable
     .flatMap(Func1<ArrayList<Gist>, Observable<out Gist>> { Observable.from(it) })
     .filter { it.owner != null }

In Kotlin:

listOfItems.filter {
    it.owner != null
}

filter internally is Extension Function of Iterable<T> which iterate over list filtering it and returns filtered list.

3. Zip

In Rx:

Observable.zip(
        observable,
        loadFeedviaRx2(),
        Func2<ArrayList<Gist>, ArrayList<Gist>, ArrayList<Gist>> { list1, list2 ->
            // here we get both the results at a time.
            return@Func2 combinedList(list1,list2)
        })
fun loadFeedviaRx2(): Observable<ArrayList<Gist>>? {

    return  RetrofitSingleton.getInstance()!!.provideClient()
            .gistsObservable.subscribeOn(Schedulers.io())
            .observeOn(AndroidSchedulers.mainThread())

}

In Kotlin:

listOfItems.zip(loadFeedWithoutRx()) // returns  List<Pair<Gist, MyGist>>
suspend fun loadFeedWithoutRx(): ArrayList<MyGist> {
    return listOfItems

4. Map

I need to map Gist to MyGist

In Rx:

observable.flatMap(Func1<ArrayList<Gist>, Observable<out Gist>> { Observable.from(it) })
.map(Func1<Gist, MyGist> { MyGist(it) })

In Kotlin:

listOfItems
       .map {
            MyGist(it)
        } 

5. Distinct

In Rx:

observable.observeOn(AndroidSchedulers.mainThread())
.map(Func1<Gist, MyGist> { MyGist(it) })
.toList()
.distinct()

In Kotlin:

listOfItems.map {
    MyGist(it)
}.distinct()

5. Buffer(Splitting into chunks)

In Rx:

 observable
        .flatMap(Func1<ArrayList<Gist>, Observable<out Gist>> { Observable.from(it) })
        .filter { it.owner != null }
        .map(Func1<Gist, MyGist> { MyGist(it) })
        .toList()
        .buffer(3) //returns Observable<MutableList<MutableList<MyGist>>>? 

In Kotlin:

listOfItems.filter {
    it.owner != null
}.map {
    MyGist(it)
}.chunked(3) //returns ArrayList<List<MyGist>>