extension for KVO

KVOBinding.swift

extension NSObjectProtocol where Self: NSObject {

    func observe<Value>(_ keyPath: KeyPath<Self, Value>,
                        onChange: @escaping (Value?) -> Void) -> NSKeyValueObservation {
        return observe(keyPath, options: [.initial, .new]) { _, change in
            onChange(change.newValue)
        }
    }

    func bind<Value, Target>(_ sourceKeyPath: KeyPath<Self, Value>,
                             to target: Target,
                             at targetKeyPath: ReferenceWritableKeyPath<Target, Value>) -> NSKeyValueObservation {
        return observe(sourceKeyPath) { (value) in
            guard let newValue = value else { return }
            target[keyPath: targetKeyPath] = newValue
        }
    }
}