PropertyWrapper: Automatically redraw UIViews when a value changes

Redraw.swift

@propertyWrapper
struct Redraw<Value> {
    var wrappedValue: Value

    init(wrappedValue: Value) {
        self.wrappedValue = wrappedValue
    }

    static subscript<Instance: UIView>(
        _enclosingInstance instance: Instance,
        wrapped wrappedKeyPath: ReferenceWritableKeyPath<Instance, Value>,
        storage storageKeyPath: ReferenceWritableKeyPath<Instance, Self>
    ) -> Value {
        get { instance[keyPath: storageKeyPath].wrappedValue }
        set {
            instance[keyPath: storageKeyPath].wrappedValue = newValue
            instance.setNeedsDisplay()
        }
    }
}


// Usage
class MyView: UIView {
    @Redraw var font = UIFont.systemFont(ofSize: 10)
}

let instance = MyView()
print(instance.font)
instance.font = .boldSystemFont(ofSize: 40)
print(instance.font)

Redraw_Alternative.swift

// This one tracks changes to the value and attempts a refresh with any mutations
@propertyWrapper
struct Redraw<Value: UIView> {
    @dynamicMemberLookup
    struct Box {
        private var value: Value
        init(_ value: Value) {
            self.value = value
        }
        subscript<T>(dynamicMember keyPath: ReferenceWritableKeyPath<Value, T>) -> T {
            get { value[keyPath: keyPath] }
            set {
                value[keyPath: keyPath] = newValue
                value.superview?.setNeedsDisplay()
            }
        }
    }
  
    var wrappedValue: Box
  
    init(wrappedValue: Value) {
        self.wrappedValue = .init(wrappedValue)
    }
    init(wrappedValue: Box) {
        fatalError("Please create with an instance of `\(type(of: Value.self))")
    }
}

// Usage
class MyView: UIView {
    @Redraw var label = UILabel()
}

let instance = MyView()
instance.label.text = "Foo" // this will trigger a refresh