Emerging Best Practices in Swift

Transcript

1. 1.

   Emerging Best Practices in Swift Ash Furrow

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   None
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   Afraid I was

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   Fine Everything turned out

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   Best Practices in Swift

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   What do they look like? Also, how do we find

   new ones?
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   Agenda • We’ve been here before • Learning is forever,

   deal with it • Never throw ideas away • How to force yourself to think • Always be abstracting
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   Let’s go!

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   This looks strangely familiar…

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    —Lots of people, for hundreds of years “Those who don’t

    study history are doomed to repeat it.”
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    Wow, that’s depressing.

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    —Me, today “Those who don’t understand the past can’t make

    informed decisions about the present.”
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    iOS 5 or earlier?

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    Before Object Literals NSArray *array = [NSArray arrayWithObjects: @"This", @"is",

    @"so", @"tedious", nil]; NSDictionary *dictionary = [NSDictionary dictionaryWithObjectsAndKeys: @"Who would do this?", @"Not me", nil]; NSNumber *number = [NSNumber numberWithInt:401];
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    Before Object Literals and ARC NSArray *array = [[NSArray arrayWithObjects:

    @"This", @"is", @"so", @"tedious", nil] retain]; NSDictionary *dictionary = [[NSDictionary dictionaryWithObjectsAndKeys: @"Who would do this?", @"Not me", nil] retain]; NSNumber *number = [[NSNumber numberWithInt:401] retain];
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    None
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    After Object Literals NSArray *array = 
 @[ @"This", @"is",

    @"much", @"better" ]; NSDictionary *dictionary = 
 @{ @"Who likes this?": @"Me!" }; NSNumber *number = @(401);
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    Object Literals • Clearly way better • Adopted by everyone

    almost immediately • Became a “best practice”
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    ^{

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    Blocks & GCD • Introduced in iOS 4 • Adopted

    slowly, but surely • Required new ways of thinking • Did using blocks became a “best practice”? • Sort of…
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    Enable Blocks other best practices

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    ^{ Functional Reactive Programming Futures Promises Collections Operations Callbacks Inline

    Network Operations Generic Datasource Objects Deferred Customization Contextual Code Execution
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    Embrace Change

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    Swift 2

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    Swift 2 • Lots of new syntax • New syntax

    lets us do new things • However! Syntax is only a tool • Like blocks, Swift 2 syntax is most useful when it enables new ideas
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    Swift 2 • guard • defer • throws • etc…

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    Should I use guard?

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    What can I do with guard?

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    Examples

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    Pyramid of Doom if let thing = optionalThing { if

    thing.shouldDoThing { if let otherThing = thing.otherThing { doStuffWithThing(otherThing) } } }
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    Clause Applause if let thing = optionalThing, let otherThing =

    thing.otherThing where thing.shoudDoThing { doStuffWithThing(otherThing) }
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    Avoid Mutability func strings( parameter: [String], startingWith prefix: String) ->

    [String] { var mutableArray = [String]() for string in parameter { if string.hasPrefix(prefix) { mutableArray.append(string) } } return mutableArray } ಠ_ಠ
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    Avoid Mutability func strings( parameter: [String], startingWith prefix: String) ->

    [String] { return parameter.filter { $0.hasPrefix(prefix) } }
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    Currying • One of those weird words you avoid because

    people who say it are sometimes jerks • It’s actually a pretty straightforward concept • Currying is a function that returns another function • Useful for sharing code that’s mostly the same
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    Before Currying func containsAtSign(string: String) -> Bool { return string.characters.contains("@")

    } ... input.filter(containsAtSign)
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    Currying func contains(substring: String) -> (String -> Bool) { return

    { string -> Bool in return string.characters.contains(substring) } } ... input.filter(contains("@"))
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    Currying func contains(substring: String)(string: String) -> Bool { return string.characters.contains(substring)

    } ... input.filter(contains("@"))
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    Extract Associated Values • Use Swift enums • Attach associated

    values • Extract using a case
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    Extract Associated Values enum Result { case Success case Failure(reason:

    String) } switch doThing() { case .Success: print("") case .Failure(let reason): print("Oops: \(reason)") }
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    Extract Associated Values enum Result { case Success case Failure(reason:

    String) } if case .Failure(let reason) = doThing() { print(" \(reason)") }
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    Syntax That’s all just

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    Ideas What matters are

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    Protocol-Oriented Programming

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    … just go watch the WWDC video.

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    Others Let’s ask

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    Syntax vs Idea • How to tell if something is

    universally a good idea, or just enables other ideas? • You can’t • It’s a false dichotomy • I lied to you • I’m so sorry
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    Try stuff You’ve just got to

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    Ideas Never throw away

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    Never Throw Away Ideas • Swift was released • We

    treated Swift like object literals instead of like blocks • Some of us thought Swift was universally better • My fault, oops
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    Merit Older ideas have

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    A lot iOS developers throw things away

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    Why?

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    Beginner learns thing Is bad at thing Blames thing Thing

    must be bad
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    Beginner gets more experience New thing comes out Learning new

    thing is easier than old thing New thing must be good
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    Appealing New ideas are

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    Always a fresh supply of old APIs for us to

    blame iOS is constantly changing
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    Refactoring Let’s talk about

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    None
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    What is Not Refactor? • Refactoring does not add new

    functionality • Refactoring does not change a type’s interface • Refactoring does not change a type’s behaviour
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    Changing a unit test? Refactoring Rewriting No Yes

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    Bad Rewrites are

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    None
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    Favour incremental change

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    Code isn’t necessarily valuable But throwing it away is dangerous

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    Things to never throw away: Code Ideas &

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    Change Unit tests will help

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    Unit Testing & Thinking • So, uhh, unit testing •

    Controversial in iOS • Not so much everywhere else • Why? • We’ll get to that
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    Benefits of Testing • (Let’s presume that unit testing is

    a good idea) • I really don’t care that much about the tests • I care more about how writing tests makes me think about what I’m writing
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    Benefits of Testing • Limited object scope is good •

    High cohesion, low coupling • How to limit scope? • Controlling public interface and dependencies
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    Dependency injection?

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    Dependency Injection • €5 word for a ¢5 idea •

    Your things shouldn’t create the things they need
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    Example

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    Without Dependency Injection class ViewController: UIViewController { let networkController =

    NetworkController() func viewDidLoad() { super.viewDidLoad() networkController.fetchStuff { self.showStuff() } } }
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    With Dependency Injection class ViewController: UIViewController { var networkController: NetworkController?

    func viewDidLoad() { super.viewDidLoad() networkController?.fetchStuff { self.showStuff() } } }
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    Dependency Injection • Rely on someone else to configure your

    instance • Could be another part of your app (eg: prepareForSegue) • Could be a unit test • Protocols work really well for this
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    Dependency Injection protocol NetworkController { func fetchStuff(completion: () -> ())

    } ... class APINetworkController: NetworkController { func fetchStuff(completion: () -> ()) { // TODO: fetch stuff and call completion() } }
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    Dependency Injection protocol NetworkController { func fetchStuff(completion: () -> ())

    } ... class TestNetworkController: NetworkController { func fetchStuff(completion: () -> ()) { // TODO: stub fetched stuff completion() } }
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    Dependency Injection • Use of protocols limits coupling between types

    • Adding a method to a protocol becomes a decision you have to make • Dependency injection can also be used for shared state, like singletons
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    Without Dependency Injection func loadAppSetup() { let defaults = NSUserDefaults.standardUserDefaults()

    if defaults.boolForKey("launchBefore") == false { runFirstLaunch() } }
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    How would you even test that?

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    With Dependency Injection func loadAppSetup(defaults: NSUserDefaults) { if defaults.boolForKey("launchBefore") ==

    false { runFirstLaunch() } }
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    Don’t be an ideologue

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    Cheat with Dependency Injection func loadAppSetup( defaults: NSUserDefaults = .standardUserDefaults()){

    if defaults.boolForKey("launchBefore") == false { runFirstLaunch() } }
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    Cheat with Dependency Injection loadAppSetup() // In your app loadAppSetup(stubbedUserDefaults)

    // In your tests
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    Cheat with Dependency Injection class ViewController: UIViewController { lazy var

    networkController: NetworkController = APINetworkController() func viewDidLoad() { super.viewDidLoad() networkController.fetchStuff { self.showStuff() } } }
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    —Mackenzie King (Canada’s Winston Churchill) “TDD if necessary, but not

    necessarily TDD.”
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    Unit Testing • Don’t test private functions • Also, start

    marking functions as private • Remember, we want to avoid rewriting • Don’t test the implementation • Don’t use “partial mocks” • See @searls post on partial mocks
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    Unit Testing • So why don’t iOS developers do unit

    testing? • It’s unfamiliar and no one forces us to do it
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    Better Testing code makes me a Developer

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    Everything Abstract

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    Two or more lines of repeated code? Find a better

    way
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    (╯°□°）╯︵ ┻━┻

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    Look for Abstractions • You’re already learning new syntax •

    Look for new abstractions along the way • Not all ideas will work out • But you should still do it • Experiment!
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    No such thing Failed experiment as a

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    None
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    Learn Always opportunities to

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    Wrap Up • We have a history of being awesome,

    let’s keep it up • Learning isn’t just for when Xcode is in beta • Ideas are more valuable than code, but throwing away either is dangerous • Effective unit tests make it easy to change code • Operate at the highest level of abstraction you can at any given time
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    Make Tomorrow Better Mistakes