Reimplementing @invalidating

MyCoolInvalidating.swift

import UIKit

struct InvalidationOptions: OptionSet {
    static let constraints  = InvalidationOptions(rawValue: 1)
    static let layout       = InvalidationOptions(rawValue: 1 << 1)
    static let display      = InvalidationOptions(rawValue: 1 << 2)
    let rawValue: Int8
}

@propertyWrapper
struct MyCoolInvalidating<Value: Equatable> {
    
    static subscript<EnclosingSelf: UIView> (
        _enclosingInstance instance: EnclosingSelf,
        wrapped wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Value>,
        storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Self>
    ) -> Value {
        get { instance[keyPath: storageKeyPath].storage }
        set {
            let oldValue = instance[keyPath: storageKeyPath].storage
            instance[keyPath: storageKeyPath].storage = newValue
            
            guard oldValue != newValue else { return }
            
            let options = instance[keyPath: storageKeyPath].options
            if options.contains(.constraints) {
                instance.setNeedsUpdateConstraints()
            }
            if options.contains(.layout) {
                instance.setNeedsLayout()
            }
            if options.contains(.display) {
                instance.setNeedsDisplay()
            }
        }
    }
    
    @available(*, unavailable, message: "This property wrapper can only be applied to classes")
    var wrappedValue: Value {
        get { fatalError() }
        set { fatalError() }
    }
    
    private var storage: Value
    private var options: InvalidationOptions
    init(wrappedValue: Value, _ options: InvalidationOptions) {
        storage = wrappedValue
        self.options = options
    }
}

class MyCoolView: UIView {
    @MyCoolInvalidating(.display)
    var color: UIColor = .red
    
    override func draw(_ rect: CGRect) {
        color.setFill()
        UIRectFill(rect)
    }
    
    override func didMoveToWindow() {
        super.didMoveToWindow()
        let tap = UITapGestureRecognizer(target: self, action: #selector(tap(_:)))
        addGestureRecognizer(tap)
    }
    
    @IBAction private func tap(_ sender: Any) {
        color = UIColor(hue: CGFloat.random(in: 0...1), saturation: 1, brightness: 1, alpha: 1)
    }
}