ReactiveCocoa - Functional Reactive Programming concepts in iOS
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I have put together some slides trying to explain to a "functional reactive programming virgin" some concepts regarding functional programming, why it is being used, who is using it, what does it solve, along with some ReactiveCocoa examples - the most used FRP solution in iOS.
![- (RACSignal *) generateCats {
return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber>
subscriber) {
// my long async call ——————————————————————————-
[[MyCameraManager sharedInstance]
takePicturesBurstMode:^(UIImage *image, NSError *error) {
if (error) {
[subscriber sendError:error];
}
else {
[subscriber sendNext:image];
[subscriber sendCompleted];
}
}];
// ——————————————————————————————————————————————
return nil;
}];
}
1) take pictures](https://image.slidesharecdn.com/rac-151017091351-lva1-app6891/85/ReactiveCocoa-Functional-Reactive-Programming-concepts-in-iOS-25-320.jpg)
![- (UIImage *) applyFilter(UIImage *) {
return ;
}
[[signalFactory generateCats]
map:^id(UIImage *cat) {
return applyFilter(cat);
}];
2) apply filter](https://image.slidesharecdn.com/rac-151017091351-lva1-app6891/85/ReactiveCocoa-Functional-Reactive-Programming-concepts-in-iOS-26-320.jpg)
![- (UIImage *) putFrame(UIImage *)image {
return image ;
}
[[[signalFactory generateCats]
map:^id(UIImage *cat) {
return applyFilter(cat);
}]
map:^id(UIImage *cat) {
return putFrame(cat);
}];
3) put frame](https://image.slidesharecdn.com/rac-151017091351-lva1-app6891/85/ReactiveCocoa-Functional-Reactive-Programming-concepts-in-iOS-27-320.jpg)
![[[[[[signalFactory generateCats]
map:^id(UIImage *cat) {
return applyFilter(cat);
}]
map:^id(UIImage *cat) {
return putFrame(cat);
}]
collect] // combine all next events into one NSArray
flattenMap:^RACStream *(NSArray *allCats) {
// [signalFactory sendAsyncToBackend:allCats] is a RACSignal
return [signalFactory sendAsyncToBackend:allCats];
}]; // this will still be a RACSignal
4) Send to back for generating animated GIF](https://image.slidesharecdn.com/rac-151017091351-lva1-app6891/85/ReactiveCocoa-Functional-Reactive-Programming-concepts-in-iOS-28-320.jpg)
![[[[[[[signalFactory generateCats] // take pictures
map:^id(UIImage *cat) {
return applyFilter(cat);
}] // apply filter
map:^id(UIImage *cat) {
return putFrame(cat);
}]] // put frame
collect] // get all the processed images
flattenMap:^RACStream *(NSArray *allCats) {
return [signalFactory sendAsyncToBackend:allCats];
}] // send async call and wait for the result
// signal is started when someone subscribes
subscribeNext:^(UIImage *animatedGIF) {
// success!, display GIF
}
error:^(NSError *error) {
// error
}];
5) see the result](https://image.slidesharecdn.com/rac-151017091351-lva1-app6891/85/ReactiveCocoa-Functional-Reactive-Programming-concepts-in-iOS-29-320.jpg)
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ReactiveCocoa - Functional Reactive Programming concepts in iOS
- 1. ReactiveCocoa functional reactive programming in iOS Andrei Popa
- 2. A. current challenges in programming - keeping state, inputs, asynchronous tasks, callback hell B. how does Functional Reactive Programming solve them - the functional aspect - the reactive aspect C. ReactiveCocoa - mature FRP implementation for iOS D. Examples
- 3. - the input is all the sources of action for your app: button taps, keyboard events, timer triggers, GPS events, web service responses, etc. - the output at any one time is the result of combining all inputs. - ft (input) = output - but unlike the classic input / output design, this input and output happens more than once. It’s not just a single input - work - output, the cycle continues while the app is open first problem: state
- 4. first problem: state And so our only tool for dealing with all these different things is state.
- 6. • obviously this is highly error prone • to make matters worse, this type of code will often produce bugs that are incredibly hard, if not impossible to identify in any automated way • state introduces complexity. And worse, it introduces complexity that grows more than linearly with the size of our app first problem: state
- 8. nondeterministic vs deterministic - most developers have experienced the problems of non- determinism when a client calls in with a problem, but the problem is not reproducible even by retracing the exact same steps - if the program was deterministic, then retracing those exact steps would always produce the error, no exception - for testing and quality assurance purposes, reproducibility is essential
- 9. types of inputs - iOS
- 10. asynchronous operations - network requests - resource loading - image processing - bluetooth operations - file I/O What happens when several different asynchronous operations must be executed in some set order (serialized)?
- 11. asynchronous operations callback hell aka Pyramid of Doom
- 12. asynchronous operations callback hell aka Pyramid of Doom
- 13. functional programming = stateless programming - fundamental operation is the application of functions to arguments. - passing functions and blocks as objects - there is no mutable state in functional programming - f (input) = output , always produces the same output given the same input. Always. - it doesn’t rely / change on data outside the current function
- 14. functional programming = stateless programming
- 15. If we had machines that had infinite computational power, what problems would we be able to solve? - Alonzo Church developed λ - lambda calculus Computability described via λ-calculus gave rise to Functional Programming - Alan Turing developed Turing machine Computability via Turing machines gave rise to Imperative Programming. Church-Turing thesis: The notion of intuitive computability is exactly captured by λ-definability or by Turing computability.
- 16. who is using functional programming ? Some of the most complex systems written using Erlang: - telecommunication and traffic control systems - Ericsson (highly tolerant and scalable telecommunication switches) - Facebook (Facebook chat backend) - T-Mobile (advanced call control services) - WhatsApp server - average of 8 billion inbound messages and 12 billion outbound messages a day - WhatsApp scales up to more than a million connections on a single box thanks to Erlang’s amazing scalability
- 17. reactive programming In computing, reactive programming is a programming paradigm oriented around data flows and the propagation of change. We don’t care how it happens – just that we can rely on its truthfulness.
- 18. functional reactive programming time-varying values - lets us define our app in terms of the time-varying values and ensures changes propagate as needed. - the result of asynchronous work is really just a time-varying value that only has a value once the work is done - a UI element’s value could be seen as a time-varying value that changes as the user interacts with it - if my app is running on a mobile device, the device’s GPS coordinates is a time-varying value
- 19. 1. model any reaction to any event using signals - wrap calls in RACSignal (ObjC) / SignalProducer (Swift) 2. manipulate, transform, combine values sent by signals - map, filter, flattenMap, zip, concat, merge, … - throttle, delay, repeat, then, take, distinctUntilChanged, … - deliverOn(someThread), subscribeOn(someOtherThread) - subscribe ReactiveCocoa provides a common interface for all events : signal
- 20. ReactiveCocoa unifies all of Cocoa’s common patterns for asynchrony and event handling
- 21. ReactiveCocoa unifies all of Cocoa’s common patterns for asynchrony and event handling
- 23. Examples
- 24. 1) Take pictures burst mode 2) Apply filter 3) Put frame 4) Send to back for generating animated GIF
- 25. - (RACSignal *) generateCats { return [RACSignal createSignal:^RACDisposable *(id<RACSubscriber> subscriber) { // my long async call ——————————————————————————- [[MyCameraManager sharedInstance] takePicturesBurstMode:^(UIImage *image, NSError *error) { if (error) { [subscriber sendError:error]; } else { [subscriber sendNext:image]; [subscriber sendCompleted]; } }]; // —————————————————————————————————————————————— return nil; }]; } 1) take pictures
- 26. - (UIImage *) applyFilter(UIImage *) { return ; } [[signalFactory generateCats] map:^id(UIImage *cat) { return applyFilter(cat); }]; 2) apply filter
- 27. - (UIImage *) putFrame(UIImage *)image { return image ; } [[[signalFactory generateCats] map:^id(UIImage *cat) { return applyFilter(cat); }] map:^id(UIImage *cat) { return putFrame(cat); }]; 3) put frame
- 28. [[[[[signalFactory generateCats] map:^id(UIImage *cat) { return applyFilter(cat); }] map:^id(UIImage *cat) { return putFrame(cat); }] collect] // combine all next events into one NSArray flattenMap:^RACStream *(NSArray *allCats) { // [signalFactory sendAsyncToBackend:allCats] is a RACSignal return [signalFactory sendAsyncToBackend:allCats]; }]; // this will still be a RACSignal 4) Send to back for generating animated GIF
- 29. [[[[[[signalFactory generateCats] // take pictures map:^id(UIImage *cat) { return applyFilter(cat); }] // apply filter map:^id(UIImage *cat) { return putFrame(cat); }]] // put frame collect] // get all the processed images flattenMap:^RACStream *(NSArray *allCats) { return [signalFactory sendAsyncToBackend:allCats]; }] // send async call and wait for the result // signal is started when someone subscribes subscribeNext:^(UIImage *animatedGIF) { // success!, display GIF } error:^(NSError *error) { // error }]; 5) see the result
- 33. ReactiveCocoa Bindings in MVVM architecture using RAC Signals
- 34. - http://rxmarbles.com/ - http://www.sprynthesis.com/2014/06/15/why-reactivecocoa/ - http://www.sprynthesis.com/2014/12/06/reactivecocoa-mvvm- introduction/ - http://www.raywenderlich.com/62699/reactivecocoa-tutorial-pt1 - https://developers.soundcloud.com/blog/building-the-new-ios-app-a- new-paradigm - https://github.com/popaaaandrei/StarterProject_RACSwift2 The end. Thank you! Q&A