The basics of Reactive Cocoa. The tips and tricks in this presentation will cover almost all the use cases for Reactive Cocoa. Demo here: https://github.com/rob-brown/Demos/tree/master/RACDemo.

1. Reactive Cocoa
Robert Brown
Twitter: @robby_brown ADN: @robert_brown

2. What is Reactive Cocoa?
A framework for Functional Reactive Programing (FRP)
Developed by GitHub

3. What is Functional Reactive
Programming?

4. –Wikipedia
“Functional reactive programming (FRP) is a
programming paradigm for reactive programming
using the building blocks of functional
programming.”

5. What are the building blocks
of functional programming?
!
reduce/fold
map
filter
zip
!
drop
take
concat
and more

6. What is functional
programming?
Immutable data
Limited state
Pure functions

7. Immutable Data
Data structures can’t be modified in place
Values are copied as needed
NSArray vs. NSMutableArray

8. Limited State
No global data
No side effects

9. Pure Functions
Given input X, the function always returns Y
Allows for many compiler-level optimizations

10. Higher Order Functions

11. Map
1
2
3
2
4
6
x * 2
5
6
7
x + 4

12. Reduce / Fold
1
2
3
0
Sum
136

13. How do I use Reactive
Cocoa?

14. RACSignal
RACSignal is a stream of data, possibly infinite
Its values are evaluated lazily
Signals are the most used objects in Reactive Cocoa

15. RAC as KVO
Advantages:
No more hard-coded key paths
No more comparing key paths
Code locality
Refactoring will update RAC bindings

16. RAC as KVO
Disadvantages:
Watch out for retain cycles
All objects are of type id

17. RAC as KVO
[RACObserve(self, name) subscribeNext:
^(NSString * name) {
NSLog(@“Name changed: %@”, name);
}];

18. RAC Bindings
Like Cocoa Bindings
Automatically changes properties

19. RAC Bindings
RAC(self, textField2.text) =
self.textField1.rac_textSignal;
!
RAC(self, nameField.text) =
RACObserve(self, name);

20. Tips and Tricks
Transform the values of a signal:
[signal map:^id(NSString * text) {
return [text uppercaseString];
}];

21. Tips and Tricks
Combine the results of many signals:
[RACSignal combineLatest:@[s1, s2] reduce:
^id(NSNumber * b1, NSNumber * b2) {
return @([b1 boolValue] &&
[b2 boolValue]);
}];

22. Tips and Tricks
Watch for when multiple tasks complete:
[[RACSignal merge:@[signal1, signal2]
subscribeCompleted:^{
NSLog(@“All done”);
}];

23. Tips and Tricks
Add actions to buttons:
self.button.rac_command =
[[RACCommand alloc]
initWithSignalBlock:^RACSignal *(id x) {
// Code goes here
};

24. Tips and Tricks
Create arbitrary signals:
[RACSignal createSignal:
^RACDisposable *(id<RACSubscriber> subscriber)
{
// Send next, error, and completed
// messages to subscriber
}];

25. Tips and Tricks
Deliver signal results to the main thread:
[backgroundSignal deliverOn:
[RACScheduler mainThreadScheduler]];

26. Tips and Tricks
If you need to perform side effects:
[signal doNext:^(id value) {…}];
[signal doError:^(NSError * error) {…}];
[signal doCompleted:^{…}];

27. Tips and Tricks
Limit the rate a signal can be evaluated:
[signal throttle:10.0];

28. Questions?

29. Demo

30. Want to Learn More?
GitHub
NSHipster
Ray Wenderlich

31. Other Implementations
C♯ Reactive Extensions (Rx)
JavaScript react.js