A Basic introduction to Reactive Cocoa

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Reactive Cocoa Hari Balamani Monday, 8 July 13

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reactive programming ? Monday, 8 July 13

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Monday, 8 July 13

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var x = 10; var y = 5; var z = x + y; x = 20; assert.areEqual(25, z); Monday, 8 July 13

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var x = 10; var y = 5; var z = x + y; x = 20; assert.areEqual(25, z); Monday, 8 July 13

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imperative programming var x = 10; var y = 5; var z = x + y; x = 20; assert.areEqual(25, z); Monday, 8 July 13

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var x := 10; var y := 5; var z := x + y; x := 20; assert.areEqual(25, z); Monday, 8 July 13

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var x := 10; var y := 5; var z := x + y; x := 20; assert.areEqual(25, z); Monday, 8 July 13

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reactive programming var x := 10; var y := 5; var z := x + y; x := 20; assert.areEqual(25, z); Monday, 8 July 13

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imperative programming Monday, 8 July 13

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imperative programming • tell the “machine” how to do something and as a result what you want to happen will happen Monday, 8 July 13

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imperative programming • tell the “machine” how to do something and as a result what you want to happen will happen NSArray *names = @[@"apple", @"google", @"microsoft"]; NSMutableArray *decoratedNames = [NSMutableArray array]; for (int i = 0; i < names.count; i++ ) { decoratedNames[i] = [names[i] uppercaseString]; } // decoratedNames: @[ @"APPLE", @"GOOGLE", @"MICROSOFT" ] Monday, 8 July 13

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declarative programming Monday, 8 July 13

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declarative programming • tell the “machine” what you would like to happen, and let the machine ﬁgure out how to do it Monday, 8 July 13

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declarative programming • tell the “machine” what you would like to happen, and let the machine ﬁgure out how to do it id *decoratedNames = [@[@"apple", @"google", @"microsoft"] ! ! ! ! ! map:^id(NSString *name){ ! ! ! ! ! ! return [name uppercaseString]; ! ! ! ! ! }]; // decoratedNames: @[ @"APPLE", @"GOOGLE", @"MICROSOFT" ] Monday, 8 July 13

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so what? • Increases the complexity • maintaining lots of states • unwanted templates/boilerplate codes (delegates/protocols/KVO/notoﬁcations etc) • poor code locality (where does this code belong) Monday, 8 July 13

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Reactive Programming “Programming around data ﬂows and the propagation of change” Monday, 8 July 13

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streams Monday, 8 July 13

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streams • sequence of values • values over variables • no in-place modiﬁcation Monday, 8 July 13

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signals Monday, 8 July 13

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signals • observes the streams • reacts to the past, present & future values • similar to promises / futures Monday, 8 July 13

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trace our test x y z:= x+y 10 5 15 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 5 15 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 5 20 15 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 5 20 15 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 5 20 15 30 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 5 20 15 30 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 5 20 x 15 30 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 5 20 x 15 30 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 5 20 x 15 30 40 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 5 20 x 15 30 40 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 5 20 x 25 15 30 40 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 5 20 x 25 15 30 40 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 5 20 x 25 15 30 40 50 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 x 5 20 x 25 15 30 40 50 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 x 5 20 x 25 x 15 30 40 50 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 x 5 20 x 25 x 15 30 40 50 Monday, 8 July 13

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trace our test x y z:= x+y 10 x 20 25 x 5 20 x 25 x 15 30 40 50 x Monday, 8 July 13

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Reactive Cocoa A [Cocoa] framework for composing and transforming streams of values Monday, 8 July 13

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3 key components • RACSignal • sends a sequence of events with some data • RACSubscriber • receives from signals • RACDisposable • encapsulates cleanup and deallocation Monday, 8 July 13

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RACSignal • n (arbitrary length of next) events sending data • multiple values can be sent a tuples • completion and an error event Monday, 8 July 13

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RACSubscriber • subscribe to events sent by RACSignal • a protocol that can be implemented anywhere Monday, 8 July 13

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RACSubscriber • subscribe to events sent by RACSignal • a protocol that can be implemented anywhere [RACSignal someSignal] subscribeNext:^(id x) { NSLog(@"Next event : %@", x);} completed : ^{ NSLog(@"done!");} error : ^(NSError *error){ NSLog(@"Error : %@", error); }]; Monday, 8 July 13

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Bridges • RACAble() Macro - Signals from KVO • RAC() Macro - Subscribes from Key Path • RACSubject - Mutable signal • -rac_lift_selector - Make signals from method invocations • -rac_signalForControlEvents - Signals from UIControl action • -rac_addObserverForName - Signals from Notiﬁcation center Monday, 8 July 13

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demo [email protected]:hari-tw/reactivecocoa-playground.git Monday, 8 July 13

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when to use • Handling asynchronous events • chaining dependent events • parallelizing independent work • simplifying collections transformations Monday, 8 July 13

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references • https://github.com/ReactiveCocoa/ReactiveCocoa • Input and Output – j.mp/joshaberio • https://github.com/andrewsardone/RACMobiDevDay Monday, 8 July 13

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thanks Monday, 8 July 13