Lazy stored property

関モバ#4の発表資料です．
Lazy stored propertyについて話しました．

Transcript

1. MB[ZTUPSFEQSPQFSUZ
   @yashigani
   ؔ੢ϞόΠϧΞϓϦݚڀձ#4
   

   View Slide

2. yashigani
   id:yashigani_w @yashigani
   Mobile Application Engineer
   http://yashigani.hatenablog.com
   Hatena
   

   View Slide

3. https://flic.kr/p/4L3Fz5
   What is lazy
   stored property?
   

   View Slide

4. • Swift has two types of properties
   • computed or stored
   • Indicate lazy stored property by lazy modifier
   • Lazy stored property created when it is first
   accessed
   

   View Slide

5. class Lazy {
   lazy var person: String = {
   println("lazy evaluation!")
   return "someone"
   }()
   }
   let l = Lazy()
   let person = l.person // => lazy
   evaluation!
   println(person) // => someone
   

   View Slide

6. ͳΜͷ໾ʹཱͭͷʁ
   

   View Slide

7. lazy property͕ศརͳͱ͜Ζ
   • ΠϯελϯεͷॳظԽ͕׬ྃͨ͠ޙʹ֎෦͔Β஫ೖ
   ͞ΕΔσʔλʹґଘͨ͠propertyʹରͯ͠
   • ॳظԽʹίετ͕͔͔Δ͕ɼ࢖͏͔Θ͔Βͳ͍
   

   View Slide

8. class JSONDecoder {
   private var data: NSData
   private(set) lazy var JSONObject:
   [String: AnyObject] = {
   let data = self.data
   let JSONObject: AnyObject? =
   NSJSONSerialization.JSONObjectWithData(dat
   a, options: .AllowFragments, error: nil)
   return JSONObject as? [String:
   AnyObject] ?? [:]
   }()
   init(data: NSData) {
   self.data = data
   }
   }
   

   View Slide

9. View ControllerͰେ׆༂
   • storyboardͩͱ೚ҙͷΠχγϟϥΠβ͕࢖͑ͳ͍
   • ΠχγϟϥΠβͰͳ͘prepareForSegueͰґଘ஫ೖ
   • Implicitly Unwrapped OptionalͳpropertyΛdidSet
   ͰॳظԽ͢ΔΑΓlazyʹͨ͠΄͏͕ศར
   • view͸஗Ԇϩʔυ͞ΕΔ
   

   View Slide

10. // ͜ΕΑΓ
    final class ViewController:

    UIViewController {
    var user: User!
    var client: APIClient!
    var userManager: UserManager! {
    didSet {
    user = userManager.loginUser
    client =
    APIClient(user.session)
    }
    }
    }
    

    View Slide

11. // ͬͪ͜ͷ΄͏͕͍͍ΑͶ
    final class ViewController:

    UIViewController {
    lazy var user: User =
    self.userManager.loginUser
    lazy var client: APIClient =
    APIClient(self.user.session)
    var userManager: UserManager!
    }
    

    View Slide

12. import MBProgressHUD
    // MBProgressHUDͱ͔͸͜͏͓ͯ͘͠ͱศར
    final class ViewController:
    UIViewController {
    lazy var : MBProgressHUD = {
    var HUD =
    MBProgressHUD(view: self.view)
    self.view.addSubview(HUD)
    return HUD
    }()
    }
    

    View Slide

13. ͭ·ΓMB[Z͸࠷ߴ
    

    View Slide

14. ߋʹਐΜͩઃܭ΁
    

    View Slide

15. class Lazy {
    var person: String = "someone"
    lazy var greeting: String =
    "Hello, lazy \(self.person)!"
    }
    let l = Lazy()
    l.person = "programmer"
    let person = l.person
    println(person) // => programmer
    println(l.greeting) // => Hello, lazy
    programmer
    

    View Slide

16. ͜Ε͸ςετʹ࢖͑Δ
    • ΞϓϦέʔγϣϯ͕ґଘ͢ΔϦιʔεͳͲΛ
    Contextͱͯ͠·ͱΊΔ
    • Contextͷ΋ͭϦιʔεʹґଘ͢ΔpropertyΛ

    lazy stored propertyʹ͢Δ
    • ΞϓϦέʔγϣϯͰ͸ContextΛstaticʹऔಘ͢Δ
    ͕ɼςετͰ͸֎͔Βࠩ͠ସ͑
    

    View Slide

17. // Application Context
    public class Context {
    public static let staticContext =
    Context()
    public var path: String {
    return "data.txt"
    }
    }
    // A View Controller
    final public class ViewController:
    UIViewController {
    public var context =
    Context.staticContext
    lazy public var dataStore: String =
    self.context.path
    }
    

    View Slide

18. // test code
    func testViewController() {
    class MockContext: Context {
    override var path: String

    { return "test.txt" }
    }
    let vc = ViewController()
    // ॳظԽ͞ΕΔ·͑ʹcontextΛࠩ͠ସ͑Δ
    vc.context = MockContext()
    assert(vc.dataStore == "test.txt")
    }
    

    View Slide

19. • όέπϦϨʔʹͳΓ͕ͪͳґଘͷड͚౉͠Λ

    γϯϓϧͳ࣮૷΁ͱঢ՚
    • γϯϓϧͳ࣮૷Ͱ͋Δͱͱ΋ʹςετՄೳੑΛߴ͘
    อͭ
    

    View Slide

20. ·ͱΊ
    

    View Slide

21. • lazy stored property͸ඞཁʹͳͬͨΒॳظԽ͞ΕΔ
    • جຊతʹ͍͍͔Μ͡ʹಈ͚͘Ͳɼςετ΋͠΍͍͢
    Έ͍ͨͳͷΛ࡞ΕΔ
    • lazy࠷ߴʂ͍ͪ͹Μ޷͖ͳम০Ͱ͢
    

    View Slide

22. 5PCF

    BMB[ZQSPHSBNNFS
    

    View Slide

23. ͋Γ͕ͱ͏͍͟͝·ͨ͠
    

    View Slide