Property wrappers intro

Property wrappers encapsulate get/set logic behind attribute syntax—@State, @Published, and @AppStorage in SwiftUI build on this language feature.

Custom wrapper sketch

@propertyWrapper
struct Clamped {
    private var value: Int
    let range: ClosedRange<Int>
    var wrappedValue: Int {
        get { value }
        set { value = min(max(newValue, range.lowerBound), range.upperBound) }
    }
    init(wrappedValue: Int, _ range: ClosedRange<Int>) {
        self.range = range
        self.value = min(max(wrappedValue, range.lowerBound), range.upperBound)
    }
}

Playground note

SwiftUI property wrappers need the SwiftUI framework—this lesson demonstrates the language mechanism with plain structs and print().

Important interview questions and answers

1. Q: What problem do property wrappers solve?
   A: Reusable storage and access patterns without repeating boilerplate getters/setters—validation, persistence, threading.
2. Q: projectedValue ($)?
   A: Some wrappers expose a projected value—e.g. $binding for two-way SwiftUI bindings.

Self-check

1. What attribute declares a property wrapper type?
2. Why are SwiftUI wrappers not used in sandbox code?

Tip: SwiftUI wrappers like @State build on property wrappers—explore locally in Xcode.