Lessons from Production Swift

This is a presentation I gave at Istanbul Tech Talks about my work writing Swift in production. It discusses why we need Swift, some problems I've faced using it, and how it enables new problem-solving techniques.

http://www.istanbultechtalks.com

Transcript

1. Ash Furrow, Artsy
   Lessons
   from
   Production Swift
   

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2. February, 2014
   

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3. Swift
   Let’s talk about
   

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4. 1. The Need for Swift
   2. The Fast and the Faulty
   3. Seek Out Bold New Worlds
   

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5. Need
   Swift
   The
   for
   

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6. Objective-C
   

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7. TXS ;push return address back onto stack
   LDY #$00 ;load Y with zero - will hold result
   LOOP1 LDAA TEMP ;load A into TEMP
   ANDA MASK ;AND A with Mask
   BNE ADD1
   BRA NONE1
   ADD1 INY ;increment our counter of 1's
   NONE1 LDAA TEMP ;reload accumulator A
   LSL MASK ;Shift the mask's 1 bit left
   BNE LOOP1 ;If we haven't finished our loop, branch
   LDAA #$01 ;load new mask into A
   STAA MASK ;store the reset mask into MASK
   TSX ;pull of return address and store in X
   PULA ;pull off A
   STAA TEMP ;store the value into temp
   TXS ;push return address back onto the stack
   LOOP2 LDAA TEMP ;Load A into TEMP
   ANDA MASK ;logical AND MASK with A
   BNE ADD2 ;add one if we need to
   BRA NONE2
   ADD2 INY ;increment our counter of 1's
   NONE2 LDAA TEMP
   LSL MASK ;shift our mask left by one
   BNE LOOP2 ;loop back until we've exhausted positions
   STY TEMP ;store Y into TEMP - this is the number of 1's
   LDAB TEMP ;load the number of 1's into B
   LDAA #$10 ;load dec 16 into A
   SBA ;A - B -> A same as 16 - B -> A
   

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8. —John Siracusa
   “While hardware performance increases over time,
   the human capacity to deal with complexity does not.”
   

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9. Stuck
   Objective-C
   Past
   is
   in the
   

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10. Beyond Hope
    Objective-C
    is
    

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11. Criteria
    1. No C baggage
    2. Memory Managed
    3. Native unicode strings
    4. Native collections
    5. Be concise
    6. Named Parameters
    

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12. Criteria
    1. No C baggage
    2. Memory Managed
    3. Native unicode strings
    4. Native collections
    5. Be concise
    6. Named Parameters
    
    
    
    
    
    
    

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13. The Need for Swift
    • Programming abstraction increases over time
    • Objective-C has improved all it can
    • Swift is the next step
    • Revolution, not evolution
    

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14. Fast
    Faulty
    The
    and the
    

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15. Problems In Beta
    • Xcode crashes
    • Compiler segfaults
    • Constant changes to Swift
    • Many language limitations
    

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16. Problems Now
    • Still some stability issues
    • Still frequent changes to Swift
    • Still some remaining language limitations
    

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17. Problems Now
    • Language changes tied to Xcode versions
    • Runtime changes tied to Xcode versions
    • Changes in resource-loading in frameworks
    

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18. Community Tools
    • Most still in their infancy
    • CocoaPods, Jazzy, SBConstants…
    • The rest do not exist (or are still in beta)
    • Test coverage analyzer
    

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19. Community Libraries
    • Struggling to accomodate frequent Swift changes
    • Xcode updates make this difficult
    

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20. The Fast and the Faulty
    • Swift had a rough start
    • Was to be expected
    • Things are better now
    • Mostly
    • Growing pains
    

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21. Seek Out
    New Worlds
    Bold
    

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22. Problem Solving in Objective-C
    Problem Solving in Swift
    is not
    

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23. Examples
    

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24. Index Paths
    • Used to identify cells in a table view
    • Section, row
    • Lots of horrendous code
    • It’s so bad
    • Seriously bad
    

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25. Index Paths
    if (indexPath.section == 0) {
    if (indexPath.row == 0) {
    } else if (indexPath.row == 1) {
    

    } else if ...
    } else if (indexPath.section == 1) {
    if (indexPath.row == 0) {
    } else if (indexPath.row == 1) {
    

    } else if ...
    } else if ...
    

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26. Index Paths
    switch (indexPath.section, indexPath.row) {
    case (0, 0):
    case (0, 1):
    case (1, 0):
    case (1, 1):
    default:
    // nop
    }
    

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27. Still Terrible
    This is
    

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28. Index Paths
    switch (indexPath.section, indexPath.row) {
    case (0, let row):
    // Executed for any section 0, row is row
    case (let section, 0) where section % 2 == 1:
    // Executed for first rows of odd all sections
    case (let section, let row) where validate(section):
    // Executed when validate() returns true
    default:
    // Executed on all other cases
    }
    

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29. Generics
    • Define functions, structs, others in the abstract
    • Create one instead of many
    • Arrays, dictionaries, and sets are all generics
    

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30. Generics
    struct Stack {
    private var contents = Array()
    mutating func push(value: T) {
    contents.insert(value, atIndex: 0)
    }
    mutating func pop() -> T {
    return contents.removeAtIndex(0)
    }
    var isEmpty: Bool {
    return countElements(contents) == 0
    }
    }
    

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31. Generics
    var intStack = Stack()
    var stringStack = Stack()
    var stackStack = Stack>()
    intStack.push(1)
    intStack.pop() // Returns 1
    

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32. Lazy Loading
    • Create resource when it is first accessed
    • Avoids unnecessary work for CPU
    • Avoids unnecessary memory use
    

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33. Lazy Objective-C
    • No language-level support
    • Lots of repetition
    • Tedious work
    • Lots of repetition
    

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34. Lazy Objective-C
    @interface MyClass: NSObject
    @property (nonatomic, copy) NSString *name;
    @end
    @implementation
    - (NSString *)name {
    if (_name == nil) {
    _name = "Ash Furrow";
    }
    return _name;
    }
    @end
    

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35. Lazy Swift
    class MyClass {
    lazy var name = "Ash Furrow"
    }
    

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36. Lazy Swift
    class MyClass {
    lazy var name = "Ash Furrow"
    }
    MyClass().name // Returns "Ash Furrow"
    let instance = MyClass()
    instance.name = "Orta Therox"
    instance.name // Returns “Orta Therox"
    

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37. Lazy Swift
    class MyClass {
    lazy var name = "Ash Furrow”
    lazy var greeting: String = {
    return "Hello, \(self.name)"
    }()
    }
    MyClass().greeting // Returns "Hello, Ash Furrow"
    let instance = MyClass()
    instance.name = "Orta Therox"
    instance.greeting // Returns "Hello, Orta Therox"
    instance.name = "Eloy Durán"
    instance.greeting // Returns "Hello, Orta Therox"
    

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38. Extending Types
    • Objective-C has “categories” for extending
    existing classes
    • Swift has “extensions” instead
    • They work on all types
    

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39. Extending Types
    extension Int {
    func times(closure: () -> ()) {
    for i in 0..closure()
    }
    }
    }
    4.times {
    // Do something 4 times
    }
    

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40. Extending Types
    extension Int {
    var hours: NSTimeInterval {
    return NSTimeInterval(3600 * self)
    }
    }
    extension NSTimeInterval {
    var fromNow: NSDate {
    return NSDate(timeIntervalSinceNow: self)
    }
    var ago: NSDate {
    NSDate(timeIntervalSinceNow: -self)
    }
    }
    4.hours.fromNow
    4.hours.ago
    

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41. Functional Awesomeness
    let people = ["Carter", "Sebastian", "Daniel"]
    people.map { "Hello, \($0)!" }
    func hello(name: String) -> String {
    return "Hello, \(name)!"
    }
    people.map(hello)
    or…
    

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42. Functional Awesomeness
    func say(greeting: String) -> (name: String) -> String {
    return { (name: String) -> String in
    "(greeting), \(name)!"
    }
    }
    people.map(say("Hello"))
    people.map(say("Merhaba"))
    

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43. Functional Awesomeness
    func say(greeting: String)(name: String) -> String {
    return "(greeting), \(name)!"
    }
    people.map(say("Hello"))
    people.map(say("Merhaba"))
    

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44. SBConstants
    • Generate constants for Storyboard identifiers
    • Compile-time checked enum
    • Can be extended…
    

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45. SBConstants
    func performSegue(identifier: SegueIdentifier) {
    performSegueWithIdentifier(identifier.rawValue, sender: self)
    }
    ...
    func ==(lhs: UIStoryboardSegue, rhs: SegueIdentifier) -> Bool {
    return lhs.identifier == rhs.rawValue
    }
    

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46. SBConstants
    peformSegue(.RegisterCreditCard)
    ...
    func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    if segue == .RegisterCreditCard {
    ...
    }
    }
    

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47. SBConstants
    • Don’t use rawValue all over the place
    • Abstract it away
    • Get compile-time safety
    

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48. Familiar Problems
    New Ways
    to solve
    Let’s look for
    

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49. For Advice
    Ask
    other communities
    Let’s
    

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50. Resources
    • Natasha the Robot’s newsletter
    • iOSDevWeekly
    • iOS Goodies
    • GitHub Explore
    • leanpub.com/yourfirstswiftapp
    

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51. Eidolon
    

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52. 1. The Need for Swift
    2. The Fast and the Faulty
    3. Seek Out Bold New Worlds
    

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53. Better Mistakes
    Make
    Tomorrow
    

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