Reactive and Functional Programming

Reactive and Functional Programming
Tales of failure and learning

Slides from my talk at Software Craftsmanship Florianópolis (Sept. 2, 2017). The talk contains some lessons learned during my experience with learning and evolving with Reactive Programming, Functional Programming and RxJava.

Transcript

1. Reactive and Functional Programming David Tiago Conceição Involves Android Dev BR @davidtiagocon Tales of failure and learning
2. Once upon a time...
3. Asynchronous code • Callbacks
4. Asynchronous code • Callbacks someObject.longNetworkOperation( new NetworkOperationCallback() { void onOperationResult(Result result) { updateScreen(result); } });
5. Asynchronous code • Callbacks someObject.longNetworkOperation( new NetworkOperationCallback() { void onOperationResult(Result result) { updateScreen(result); } void onSomethingWentWrong(WhatWentWrong what) { showError(what); } });
6. Asynchronous code • Callbacks someObject.longNetworkOperation( new NetworkOperationCallback(){ void onOperationResult(Result result){ anotherObject.doAnotherLongOperation( result, new NetworkOperationCallback(){ void onOperationResult(Result result){ finallyShowTheResult(result); ...
7. Asynchronous code • Callbacks someObject.longNetworkOperation( new NetworkOperationCallback(){ void onOperationResult(Result result){ anotherObject.doAnotherLongOperation( result, new NetworkOperationCallback(){ void onOperationResult(Result result){ finallyShowTheResult(result); } void onSomethingWentWrong(WhatWentWrong what){ showError(what); } } } void onSomethingWentWrong(WhatWentWrong what){ showError(what); } });
8. Asynchronous code • Callbacks someObject.longNetworkOperation( new NetworkOperationCallback(){ void onOperationResult(Result result){ anotherObject.doAnotherLongOperation( result, new NetworkOperationCallback(){ void onOperationResult(Result result){ runOnUiThread(new Runnable(){ void run(){ finallyShowTheResult(result); } }); } void onSomethingWentWrong(WhatWentWrong what){ runOnUiThread(new Runnable(){ showError(what); }); } } } void onSomethingWentWrong(WhatWentWrong what){ showError(what); } });
9. Asynchronous code • Callbacks someObject.longNetworOperation( new NetworkOperationCallback(){ void onOperationResult(Result result){ anotherObject.doAnotherLongOperation( result, new NetworkOperationCallback(){ void onOperationResult(Result result){ runOnUiThread(new Runnable(){ void run(){ finallyShowTheResult(result); } }); } void onSomethingWentWrong(WhatWentWrong what){ runOnUiThread(new Runnable(){ showError(what); }); } } } void onSomethingWentWrong(WhatWentWrong what){ showError(what); } }); https://storage.googleapis.com/material-design/publish/material_v_11/assets/0Bzhp5Z4wHba3NnpEM2lLc0NKd1U/notifications_templates_04_progress.png
10. Asynchronous code
11. Asynchronous code • AsyncTasks private class NetworkOperation extends AsyncTask<Input, Integer, Long> { protected Long doInBackground(Input... inputs) { return someLongNetworkOperation(inputs); } protected void onProgressUpdate(Integer... progress) { setProgressPercent(progress[0]); } protected void onPostExecute(Long result) { showDialog("Downloaded " + result + " bytes"); } }
12. Asynchronous code • IntentService public class NetworkService extends IntentService { @Override protected void onHandleIntent(Intent workIntent) { longNetworkOperation(workIntent); } }
13. Asynchronous code
14. https://thumb7.shutterstock.com/display_pic_with_logo/164459732/518981521/stock-photo-react-stamp-sign-text-word-logo-black-518981521.jpg
15. Reactive Extensions “An API for asynchronous programming with observable streams.” http://reactivex.io/
16. Reactive Extensions “An API for asynchronous programming with observable streams.” “The Observer pattern done right.” http://reactivex.io/
17. RxJava • Creating an Observable Single.fromCallable(() -> { return someNetworkOperation();}) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
18. RxJava • Creating an Observable Single.fromCallable(() -> { return someNetworkOperation(); }) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
19. RxJava • Creating an Observable Single.fromCallable(() -> { return someNetworkOperation(); }) .flatMap(networkResult -> { return anotherNetworkOperation(networkResult); }) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
20. RxJava • Creating an Observable compositeDisposable = new CompositeDisposable(); // ... compositeDisposable.add(createStream()); // ... compositeDisposable.clear(); https://storage.googleapis.com/material-design/publish/material_v_11/assets/0Bzhp5Z4wHba3NnpEM2lLc0NKd1U/notifications_templates_04_progress.png
21. RxJava
22. RxJava
23. Reactive Extensions “CREATE, COMBINE, LISTEN” http://reactivex.io/
24. RxJava • Create Single.fromCallable(() -> { return someNetworkOperation();}) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
25. RxJava • Combine Single.fromCallable(() -> { return someNetworkOperation(); }) .flatMap(networkResult -> { return anotherNetworkOperation(networkResult); }) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
26. RxJava • Listen Single.fromCallable(() -> { return someNetworkOperation(); }) .flatMap(networkResult -> { return anotherNetworkOperation(networkResult); }) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
27. RxJava • Stream Single.fromCallable(() -> { return someNetworkOperation(); }) .flatMap(networkResult -> { return anotherNetworkOperation(networkResult); }) .subscribeOn(Schedulers.io()) .observeOn(AndroidSchedulers.mainThread()) .subscribeWith(new DisposableSingleObserver<NetworkResult>() { public void onSuccess(NetworkResult result) { updateScreen(result); } public void onError(Throwable e) { showError(e); } });
28. Growing Strong • Start composing ◦ Large streams composed by smaller • Less logic • More data flow
29. Growing Strong class SomeNetworkClass { Observable<NetworkResponse> longNetworkOperation(Parameters parameters){ // Compose networkParameters return NetworkLibrary.createNetworkRequest(networkParameters); } } // ... someNetworkInstance.longNetworkOperation(parameters) .doOnNext(Cache::saveToCache) .subscribeWith( // subscriber ...
30. Growing Strong class SomeNetworkClass { Observable<NetworkResponse> longNetworkOperation(Parameters parameters){ // Compose networkParameters return NetworkLibrary.createNetworkRequest(networkParameters); } } // ... someNetworkInstance.longNetworkOperation(parameters) .doOnNext(Cache::saveToCache) .subscribeWith( // subscriber ...
31. Race Conditions moviesRemoteRepository.getUpcoming(currentPageCount) .map(new Function<Movie, Movie>() { public Movie apply(Movie movie) throws Exception { return MovieUtil.mapMovieFields( movie, imageConfiguration, genres); } }) .toList() //...
32. Race conditions moviesRemoteRepository.getUpcoming(currentPageCount) .map(new Function<Movie, Movie>() { public Movie apply(Movie movie) throws Exception { return MovieUtil.mapMovieFields( movie, imageConfiguration, genres); } }) .toList() //...
33. Reactive Extensions “ReactiveX is a combination of the best ideas from the Observer pattern, the Iterator pattern, and functional programming.” http://reactivex.io/
34. Functional Programming • Mathematical concepts • High order functions • Immutability • Lambdas • Monads • Pure functions
35. Pure Functions • Output determined by the input • No side effects • An input generates always the same output
36. Pure Functions int sum(int firstNumber, int secondNumber){ return firstNumber + secondNumber; }
37. Pure Functions moviesRemoteRepository.getUpcoming(currentPageCount) .merge(//... Stream of more data .combineLatest( //... Stream of more data .toList() //...
38. Pure Functions • Easily processed in parallel ◦ Highly scalable • Independent Streams • Easy to read, maintain and test
39. Reactive Architectures • Communication through streams
40. Reactive Architectures • Communication through streams • Components reacting to each other
41. Everything as stream • User inputs • I/O • Internal events • System events
42. What could go wrong? • State, error handling, and much more
43. Propagating state • Single source of truth • Hot Observables • Mapping, flat mapping and others
44. Handling errors • onError invalidates the stream • Error as state • Propagate an error state • Avoids invalidation
45. Much more • Complex streams • Weird use cases
46. And now? • Key architectural component • Can’t work without it
47. How to know more? • ReactiveX reactivex.io • RxJava for Android App Development oreilly.com/programming/free/rxjava-for-android-app-development.csp • Reactive Programming on Android with RxJava leanpub.com/reactiveandroid • Managing State with RxJava by Jake Wharton www.youtube.com/watch?v=0IKHxjkgop4 • Object-Oriented vs. Functional Programming oreilly.com/programming/free/object-oriented-vs-functional-programming.csp
48. slack.AndroidDevBR.org Android Dev BR
49. Thank you! David Tiago Conceição Android Developer @ Involves Android Dev BR @davidtiagoconceicao twitter.com/@davidtiagocon github.com/davidtcdeveloper Slides