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Lazy stored property
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yashigani
July 27, 2015
Programming
3
2k
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.
yashigani
July 27, 2015
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Transcript
MB[ZTUPSFEQSPQFSUZ @yashigani ؔϞόΠϧΞϓϦݚڀձ#4
yashigani id:yashigani_w @yashigani Mobile Application Engineer http://yashigani.hatenablog.com Hatena
https://flic.kr/p/4L3Fz5 What is lazy stored property?
• 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
class Lazy { lazy var person: String = { println("lazy
evaluation!") return "someone" }() } let l = Lazy() let person = l.person // => lazy evaluation! println(person) // => someone
ͳΜͷʹཱͭͷʁ
lazy property͕ศརͳͱ͜Ζ • ΠϯελϯεͷॳظԽ͕ྃͨ͠ޙʹ֎෦͔Βೖ ͞ΕΔσʔλʹґଘͨ͠propertyʹରͯ͠ • ॳظԽʹίετ͕͔͔Δ͕ɼ͏͔Θ͔Βͳ͍
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 ControllerͰେ׆༂ • storyboardͩͱҙͷΠχγϟϥΠβ͕͑ͳ͍ • ΠχγϟϥΠβͰͳ͘prepareForSegueͰґଘೖ • Implicitly Unwrapped OptionalͳpropertyΛdidSet
ͰॳظԽ͢ΔΑΓlazyʹͨ͠΄͏͕ศར • viewԆϩʔυ͞ΕΔ
// ͜ΕΑΓ final class ViewController: UIViewController { var user: User!
var client: APIClient! var userManager: UserManager! { didSet { user = userManager.loginUser client = APIClient(user.session) } } }
// ͬͪ͜ͷ΄͏͕͍͍ΑͶ final class ViewController: UIViewController { lazy var user:
User = self.userManager.loginUser lazy var client: APIClient = APIClient(self.user.session) var userManager: UserManager! }
import MBProgressHUD // MBProgressHUDͱ͔͜͏͓ͯ͘͠ͱศར final class ViewController: UIViewController { lazy
var : MBProgressHUD = { var HUD = MBProgressHUD(view: self.view) self.view.addSubview(HUD) return HUD }() }
ͭ·ΓMB[Z࠷ߴ
ߋʹਐΜͩઃܭ
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
͜Εςετʹ͑Δ • ΞϓϦέʔγϣϯ͕ґଘ͢ΔϦιʔεͳͲΛ Contextͱͯ͠·ͱΊΔ • ContextͷͭϦιʔεʹґଘ͢ΔpropertyΛ lazy stored propertyʹ͢Δ •
ΞϓϦέʔγϣϯͰContextΛstaticʹऔಘ͢Δ ͕ɼςετͰ֎͔Βࠩ͠ସ͑
// 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 }
// 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") }
• όέπϦϨʔʹͳΓ͕ͪͳґଘͷड͚͠Λ γϯϓϧͳ࣮ͱঢ՚ • γϯϓϧͳ࣮Ͱ͋ΔͱͱʹςετՄೳੑΛߴ͘ อͭ
·ͱΊ
• lazy stored propertyඞཁʹͳͬͨΒॳظԽ͞ΕΔ • جຊతʹ͍͍͔Μ͡ʹಈ͚͘Ͳɼςετ͍͢͠ Έ͍ͨͳͷΛ࡞ΕΔ • lazy࠷ߴʂ͍ͪΜ͖ͳम০Ͱ͢
5PCF BMB[ZQSPHSBNNFS
͋Γ͕ͱ͏͍͟͝·ͨ͠