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