Property Wrappers

Transcript

1. Property Wrappers
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2. What are they?
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3. → New in 5.1
   → Java-like annotations
   → Can accept (generic) parameters
   → Used in SwiftUI
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4. Purpose
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5. Examples
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6. SwiftUI
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7. struct ContentView: View {
   @State private var value = 0.0
   var body: some View {
   VStack {
   Text("Value is \(value)")
   Slider(value: $value)
   }
   }
   }
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8. UIKit/
   Foundation
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9. class ViewController: UIViewController {
   @Keychain(key: "secret_info") var secretInfo = ""
   }
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10. Let's make one!
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11. @propertyWrapper
    struct TwelveOrLess {
    private var number = 0
    var wrappedValue: Int {
    get { return number }
    set { number = min(newValue, 12) }
    }
    }
    // Use
    struct S {
    @TwelveOrLess var num = 13 // 12
    }
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12. @propertyWrapper
    struct Clamped {
    private var number = 0
    private let maxNum: Int
    private let minNum: Int
    var wrappedValue: Int {
    get { return number }
    set { number = max(min(newValue, maxNum), minNum) }
    }
    }
    // Use
    struct S {
    @Clamped(maxNum: 10, minNum: 0) var num = 13 // 10
    }
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13. Projected values
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14. @propertyWrapper
    struct State {
    //...
    var projectedValue: Binding
    }
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15. struct ContentView: View {
    @State private var isDisabled = false
    var body: some View {
    OtherView($isDisabled) // Binding
    }
    }
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16. Conclusion
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17. More info
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18. → The Swift Programming Language
    → Burritos
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