Reactive CocoaRobert Brown Twitter: @robby_brown ADN: @robert_brown

What is Reactive Cocoa?

A framework for Functional Reactive Programing (FRP)

Developed by GitHub

What is Functional Reactive Programming?

–Wikipedia

“Functional reactive programming (FRP) is a programming paradigm for reactive programming

using the building blocks of functional programming.”

What are the building blocks of functional programming?

!

reduce/fold

map

filter

zip

!

drop

take

concat

and more

What is functional programming?

Immutable data

Limited state

Pure functions

Immutable Data

Data structures can’t be modified in place

Values are copied as needed

NSArray vs. NSMutableArray

Limited State

No global data

No side effects

Pure Functions

Given input X, the function always returns Y

Allows for many compiler-level optimizations

Higher Order Functions

Map

1

2

3

2

4

6

x * 2

5

6

7

x + 4

Reduce / Fold

1

2

3

0

Sum

136

How do I use Reactive Cocoa?

RACSignal

RACSignal is a stream of data, possibly infinite

Its values are evaluated lazily

Signals are the most used objects in Reactive Cocoa

RAC as KVO

Advantages:

No more hard-coded key paths

No more comparing key paths

Code locality

Refactoring will update RAC bindings

RAC as KVO

Disadvantages:

Watch out for retain cycles

All objects are of type id

RAC as KVO

[RACObserve(self, name) subscribeNext:

^(NSString * name) {

NSLog(@“Name changed: %@”, name);

}];

RAC Bindings

Like Cocoa Bindings

Automatically changes properties

RAC Bindings

RAC(self, textField2.text) = self.textField1.rac_textSignal;

!

RAC(self, nameField.text) = RACObserve(self, name);

Tips and Tricks

Transform the values of a signal:

[signal map:^id(NSString * text) {

return [text uppercaseString];

}];

Tips and TricksCombine the results of many signals:

[RACSignal combineLatest:@[s1, s2] reduce:

^id(NSNumber * b1, NSNumber * b2) {

return @([b1 boolValue] &&

[b2 boolValue]);

}];

Tips and Tricks

Watch for when multiple tasks complete:

[[RACSignal merge:@[signal1, signal2] subscribeCompleted:^{

NSLog(@“All done”);

}];

Tips and TricksAdd actions to buttons:

self.button.rac_command =

[[RACCommand alloc] initWithSignalBlock:^RACSignal *(id x) {

// Code goes here

};

Tips and TricksCreate arbitrary signals:

[RACSignal createSignal:

^RACDisposable *(id<RACSubscriber> subscriber) {

// Send next, error, and completed

// messages to subscriber

}];

Tips and Tricks

Deliver signal results to the main thread:

[backgroundSignal deliverOn:

[RACScheduler mainThreadScheduler]];

Tips and Tricks

If you need to perform side effects:

[signal doNext:^(id value) {…}];

[signal doError:^(NSError * error) {…}];

[signal doCompleted:^{…}];

Tips and Tricks

Limit the rate a signal can be evaluated:

[signal throttle:10.0];

Questions?

Demo

Want to Learn More?

GitHub

NSHipster

Ray Wenderlich

Other Implementations

C♯ Reactive Extensions (Rx)

JavaScript react.js