Download - Swift 2.2 Design Patterns CocoaConf Austin 2016

Swift 2.2 Design Patterns

COCOACONF AUSTIN APRIL 2016

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@CarlBrwn

[:]?

So, who is this idiot, anyway?

INTRODUCTION

@CarlBrwn

These mean a lot of different things to different people.

Hopefully they’re of some use to you.

WIDELY RECOGNIZED, BUT NOT UNDISPUTED

These mean a lot of different things to different people.

Hopefully they’re of some use to you.

WIDELY RECOGNIZED, BUT NOT UNDISPUTED

[:]?

Critical Concept in Software Engineering?Some think so, others disagree.

[:]?Simple Enumeration of

Weaknesses in C++See http://www.norvig.com/design-

patterns/[:]?

Just Shared Vocabulary?

So, Let’s talk about Swift (2.2 Version)

PATTERNS ARE LANGUAGE SPECIFIC

[:]?




patterns/[:]?


So, Let’s talk about Swift (2.2 Version)

& Cocoa

PATTERNS ARE LANGUAGE (& FRAMEWORK) SPECIFIC

[:]?




patterns/[:]?


Design Patterns in Swift 2.2CocoaConf Austin 2016

PATTERN SOURCES FOR TODAY

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Classic Cocoa Design Patterns as implemented in Swift



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Classic Cocoa Design Patterns as implemented in SwiftSome Gang of Four Patterns that lend

themselves to Swift



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themselves to SwiftPatterns Apple Documents for Swift



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themselves to SwiftPatterns Apple Documents for SwiftPatterns from Other Languages



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themselves to SwiftPatterns Apple Documents for SwiftPatterns from Other LanguagesInteresting/Potential Swift-specific Patterns


DELEGATE PATTERN

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Cocoa is said to favor “Composition over Inheritance.” Delegation is one of the hallmarks of that strategy. UITableViewDataSource and UITableViewDelegate are examples.

CLASSIC COCOA PATTERN


DELEGATE PATTERN

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Cocoa is said to favor “Composition over Inheritance.” Delegation is one of the hallmarks of that strategy. UITableViewDataSource and UITableViewDelegate are examples.

CLASSIC COCOA PATTERN

[:]?Eases ConstructionThis is a big reason why we don’t have to use the “Factory Pattern” in Cocoa/Swift


DELEGATE PATTERN IN SWIFT

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var myDS : UITableViewDataSource?

let myTVC = UITableViewController() let myTV = myTVC.tableView

let num = myDS?.tableView(myTV, numberOfRowsInSection: 0)

let firstHeader = myDS?.tableView?(myTV, titleForHeaderInSection: 0)


DELEGATE PATTERN IN SWIFT

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var myDS : UITableViewDataSource?

let myTVC = UITableViewController() let myTV = myTVC.tableView

let num = myDS?.tableView(myTV, numberOfRowsInSection: 0)

let firstHeader = myDS?.tableView?(myTV, titleForHeaderInSection: 0)

1Test Delegate OptionalThe delegate itself must not be nil (check with ? and don’t (EVER) use !)

2Test Method ExistsPut ? after method call to test for @optional implementation


ERROR HANDLING PATTERN

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In Cocoa, methods that produce errors take an NSError pointer parameter last parameter.

In Swift 2, this is converted to a thrown ErrorType

NEW IN SWIFT 2 - HOOKS INTO COCOA’S (NSError**)


ERROR HANDLING PATTERN

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In Cocoa, methods that produce errors take an NSError pointer parameter last parameter.

In Swift 2, this is converted to a thrown ErrorType

NEW IN SWIFT 2 - HOOKS INTO COCOA’S (NSError**)

[]Not JAva’s Throwtry on each line that might throw catch for blocks


ERROR HANDLING PATTERN IN SWIFT

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- (BOOL)removeItemAtURL:(NSURL *)URL error:(NSError **)error { NSFileManager *fileManager = [NSFileManager defaultManager]; NSURL *URL = [NSURL fileURLWithPath:@"/path/to/file"]; NSError *error = nil; BOOL success = [fileManager removeItemAtURL:URL error:&error]; if (!success) { NSLog(@"Error: %@", error.domain); } }


ERROR HANDLING PATTERN IN SWIFT

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func removeItemAtURL(URL: NSURL) throws { let fileManager = NSFileManager.defaultManager() let URL = NSURL.fileURLWithPath("/path/to/file") do { try fileManager.removeItemAtURL(URL) } catch let error as NSError { print("Error: \(error.domain)") } }

- (BOOL)removeItemAtURL:(NSURL *)URL error:(NSError **)error { NSFileManager *fileManager = [NSFileManager defaultManager]; NSURL *URL = [NSURL fileURLWithPath:@"/path/to/file"]; NSError *error = nil; BOOL success = [fileManager removeItemAtURL:URL error:&error]; if (!success) { NSLog(@"Error: %@", error.domain); } }


OBSERVER PATTERN

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Key-Value Observing lets you observe any well-behaved Cocoa property (getter/setter).

It works in Swift *As Long As* the target isKindOf: NSObject

KVO IN SWIFT


OBSERVER PATTERN IN SWIFT

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objectToObserve.addObserver(self, forKeyPath: "myDate", options: .New, context: &myContext)



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override func observeValueForKeyPath(keyPath:String?, ofObject object: AnyObject?, change: [ String : AnyObject ]?, context: UnsafeMutablePointer <Void>) {

if context == &myContext { if let newValue = change?[NSKeyValueChangeNewKey] { print("Date changed: \(newValue)") } } else { super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)

} }



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override func observeValueForKeyPath(keyPath:String?, ofObject object: AnyObject?, change: [ String : AnyObject ]?, context: UnsafeMutablePointer <Void>) {

if context == &myContext { if let newValue = change?[NSKeyValueChangeNewKey] { print("Date changed: \(newValue)") } } else { super.observeValueForKeyPath(keyPath, ofObject: object, change: change, context: context)

} }

objectToObserve.removeObserver(self, forKeyPath: "myDate", context: &myContext)


SWIFT-NATIVE KVO *MAYBE* IN SWIFT 4

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TARGET-ACTION PATTERN

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In Objective-C, we use @selector to wrap the method name when adding it as a target.

In Swift 1.x, we just used a String and still had no compiler typo checking. In Swift 2.2, we have #selector (SE-0022) and we FINALLY have compiler type checking.

OSS FTW!!

ATTACH AN ACTION TO A UI ELEMENT


TARGET-ACTION PATTERN IN SWIFT

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@objc func tappedButton(sender:UIButton!) { print("tapped button") }



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@objc func tappedButton(sender:UIButton!) { print("tapped button") } #if swift(>=2.2)

myButton.addTarget(self, action: #selector(tappedButton), forControlEvents: .TouchUpInside)

#else myButton.addTarget(self, action: "tappedButton",

forControlEvents: .TouchUpInside) #endif



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@objc func tappedButton(sender:UIButton!) { print("tapped button") } #if swift(>=2.2)

myButton.addTarget(self, action: #selector(tappedButton), forControlEvents: .TouchUpInside)

#else myButton.addTarget(self, action: "tappedButton",

forControlEvents: .TouchUpInside) #endif

1Legacy Objective-COnly @objc functions can be made #selectors


SINGLETON PATTERN

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Fairly common in Cocoa, like [UIApplication sharedApplication]

In Swift, they’re much simpler to declare (and like ObjC, never dealloc’ed).

A static type property is guaranteed to be lazily initialized only once, even when accessed across multiple threads simultaneously.

SINGLETONS: GLOBAL SHARED INSTANCE


SINGLETON PATTERN IN SWIFT

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class Singleton { static let sharedInstance = Singleton() }


SINGLETON PATTERN IN SWIFT

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class Singleton { static let sharedInstance = Singleton() }

[]Well, That Was EasyObj-C is so much more complicated

[]Not All Shared Instances Are Singletonse.g. NSFileManager


“INTROSPECTION PATTERN”

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Apple’s Docs call this a pattern. It’s pretty much the same functionality as we discussed for Delegation. In my mind, “is this a kind of X class” and “does this implement Y method” are very limited forms of Introspection.

DYNAMICALLY EXAMINE TYPES AT RUNTIME


“INTROSPECTION PATTERN”

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Apple’s Docs call this a pattern. It’s pretty much the same functionality as we discussed for Delegation. In my mind, “is this a kind of X class” and “does this implement Y method” are very limited forms of Introspection.

DYNAMICALLY EXAMINE TYPES AT RUNTIME

[]Not Very UsefulWay harder in pure Swift than ObjC. Most attempts bridge NSObjects.


API AVAILABILITY CHECKING “PATTERN”

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Swift does this at Compile time rather than Runtime (like ObjC). Calling this a “Pattern” seems like a bit of a stretch to me, but Apple does. It is indisputably useful, though.

DECIDE WHETHER AN API IS AVAILABLE


API AVAILABILITY CHECKING “PATTERN”

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Swift does this at Compile time rather than Runtime (like ObjC). Calling this a “Pattern” seems like a bit of a stretch to me, but Apple does. It is indisputably useful, though.

DECIDE WHETHER AN API IS AVAILABLE

[]Also for Swift Version #sStarting with Swift 2.2


API AVAILABILITY CHECKING “PATTERN” IN SWIFT

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if ([CLLocationManager instancesRespondToSelector:@selector(requestWhenInUseAuthorization)]) {

// Method is available for use. } else { // Method is not available. }



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let locationManager = CLLocationManager() if #available(iOS 8.0, OSX 10.10, *) { locationManager.requestWhenInUseAuthorization() } let locationManager = CLLocationManager() guard #available(iOS 8.0, OSX 10.10, *) else { return } locationManager.requestWhenInUseAuthorization()





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let locationManager = CLLocationManager() if #available(iOS 8.0, OSX 10.10, *) { locationManager.requestWhenInUseAuthorization() } let locationManager = CLLocationManager() guard #available(iOS 8.0, OSX 10.10, *) else { return } locationManager.requestWhenInUseAuthorization()



#if swift(>=2.2) let tapped = #selector(tappedButton)

#endif


VALUE TYPES/STRUCTS

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Swift structs can have methods and implement protocols much like classes, but they’re always passed by value (copied) rather than passed by reference like objects (which makes them generally thread-safe, amongst other things).

SWIFT HAS RICH VALUE-TYPES


UBIQUITOUS IMMUTABILITY

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Pretty much all Swift variables can be declared immutable (with ‘let’), not just certain types like ObjC.

Immutable variables are safer, thread-safe and side-effect free, which is one claim to fame for functional languages.

NOT JUST FOR STRING/DICT/ARRAY ANYMORE


SEPARATION OF ERRORS

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Swift has several mechanisms to keep error checking outside and separate from your business logic.

Checks often get moved from runtime to compile time, and syntax allows for checks to be isolated to avoid further complicating already-intricate code.

KEEP ERROR CHECKING AWAY FROM YOUR ALGORITHMS


SEPARATION OF ERRORS 1: if let

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Much safer than finding out the hard way at runtime.

Unless you use (!)

You don’t use (!), do you? (At least not in shipping apps…)

ENFORCES NIL-CHECK AT COMPILE TIME


SEPARATION OF ERRORS IN SWIFT 1: if let

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if let obj = obj { //business logic about object goes here }


SEPARATION OF ERRORS 2: guard

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Good for checking at the top of a method

Avoids the “if-let pyramid of doom”

LIKE if-let, BUT WITH CONTINUING SCOPE


SEPARATION OF ERRORS IN SWIFT 2: guard

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guard let obj = obj as? NSString where obj.length > 0 else { return }

//business logic about object goes here


SEPARATION OF ERRORS 3: defer

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Make sure something happens as you exit a scope

SCHEDULE SOMETHING FOR LATER


SEPARATION OF ERRORS 3: defer

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Make sure something happens as you exit a scope

SCHEDULE SOMETHING FOR LATER

[]Dearly Departed@synchronized(dict) { //use dict safely

}


SEPARATION OF ERRORS IN SWIFT 3: defer

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let lock = NSLock()

func useLock() { lock.lock() defer { lock.unlock() } //use lock }


SEPARATION OF ERRORS: try?

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The try syntax gets scattered all over your code.

Not exactly as good, but at least better than NSError** (or god forbid C’s return codes and errno).

TRY IS A COUNTER-EXAMPLE THOUGH


SEPARATION OF ERRORS IN SWIFT: try?

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let url = try fileManager.URLForDirectory(.ApplicationDirectory, inDomain: .UserDomainMask, appropriateForURL: nil, create: false)

try fileManager.removeItemAtURL( url.URLByAppendingPathComponent("/path/to/file", isDirectory: true))

if let path = url.URLByAppendingPathComponent("/path/to/file").path { let files = try fileManager.contentsOfDirectoryAtPath(path) //do something with files }


MONADS (A LA HASKELL MAYBE)

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Very complicated, at least if you believe most people.

I remember being amazed - *Really amazed* at WWDC 2014 when I realized Apple stuck a Haskell Maybe Monad into Swift, and used all of 1-character to do it.

FUNCTIONAL PROGRAMMING CONCEPT


”MAYBE” MONAD

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”MAYBE” MONAD SWIFT OPTIONAL

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Optional



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Optional

! ?



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Optional

! ?

?



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Optional

! ?

?

!



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Optional

! ?

?

!

[]“!” Considered HARMFULI mean that in a “GOTO” sense.


MAPREDUCE

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Without this, the Internet as you know it would never have come to exist, and least not when and how it did.

SEMINAL PAPER BEHIND EARLY GOOGLE

http://static.googleusercontent.com/media/research.google.com/es/us/archive/mapreduce-osdi04.pdf

http://static.googleusercontent.com/media/research.google.com/es/us/archive/mapreduce-osdi04.pdf


MAPREDUCE — MAP

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MAPREDUCE — MAP

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[]

Rule of thumbSame count, Different Type


MAPREDUCE — MAP IN SWIFT

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�

let names = ["RedStripeOnWhite.jpg","OrangeStripeOnWhite.jpg", "YellowStripeOnWhite.jpg","GreenStripeOnWhite.jpg", "BlackHorizontal.jpg","BlueStripeOnWhite.jpg", “IndigoStripeOnWhite.jpg”,"VioletStripeOnWhite.jpg"]

let images = names.map { UIImage(named: $0)

}


MAPREDUCE — MAP IN SWIFT

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�

let names = ["RedStripeOnWhite.jpg","OrangeStripeOnWhite.jpg", "YellowStripeOnWhite.jpg","GreenStripeOnWhite.jpg", "BlackHorizontal.jpg","BlueStripeOnWhite.jpg", “IndigoStripeOnWhite.jpg”,"VioletStripeOnWhite.jpg"]

let images = names.map { UIImage(named: $0)

}

1Real WorlD: JSONI use this a lot to map JSON Dict to Object/Struct, but this is more visual


MAPREDUCE — FILTER

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MAPREDUCE — FILTER

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[]

Rule of thumbSame Type, Lower Count


MAPREDUCE — FILTER IN SWIFT

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let colors = images.filter { !mono($0) }


MAPREDUCE — FILTER IN SWIFT

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let colors = images.filter { !mono($0) }

1Real WorlD: JSONI use this a lot to throw out JSON Dicts I don’t need


MAPREDUCE — REDUCE

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[]

Rule of thumbDifferent Type, Count == 1



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let rainbowImage = ciImages.reduce(CIImage()) { (s, img) -> CIImage? in let f = CIFilter(name: "CISourceOverCompositing") f?.setValue(s, forKey: kCIInputBackgroundImageKey) f?.setValue(img, forKey:kCIInputImageKey) return f?.outputImage }



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MAPREDUCE - WAIT, WAIT, WAIT!!!

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I have yet to see a case where map/reduce worked consistently faster on iOS than the equivalent for..in loop, and often it can be quite a bit slower.

BUT - learn it anyway.

ABOUT SWIFT’S MAPREDUCE PERFORMANCE…


MAPREDUCE - SO WHAT’S THE POINT?

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…or threads. Or at least, that was the design intent.

I still use it (although I don’t have to), because I’m used to it from other languages (and I use it with dispatch_groups, despite the fact they don’t fit on slides).

But Soon (SWIFT 4?? - see earlier email), we’ll have a Swift release that focuses on asynchronous functionality. And THEN, it will really, really matter.

MAPREDUCE SPLITS WORK BETWEEN MACHINES


PROTOCOL DEFAULT IMPLEMENTATIONS

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Protocol Implementations allow for much more useful protocols, and for much more flexible implementations.

WHOLE NEW WORLD


PROTOCOL EXTENSIONS (W/IMPLEMENTATIONS)

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WHOLE NEW WORLD


PROTOCOL EXTENSIONS (W/IMPLEMENTATIONS)

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WHOLE NEW WORLD

1Examples are ContrivedAnd they take a while to set up, and I’m expecting this is already going long

2Big TopicThere’s a whole (VERY GOOD) WWDC talk on just this.

Speaking to you all is always a pleasure.

Thank You