codable.decode.swift

let decoder = JSONDecoder()
if let decoded = try? decoder.decode(Episode.self, from: encoded) {
    print(decoded.title)
}

codable.encode.swift

struct Episode: Codable {
  var id: String
  var title: String
  var live: Bool
}

let whiteGold = Episode(id: 'p050hssx', title: 'White Gold', live: false)

let encoder = JSONEncoder()
if let encoded = try? encoder.encode(whiteGold) {
    print(encoded)
}

kvo-swift3.swift

class MyObject: NSObject {
    private var observerContext = 0

    var objectToObserve = Foo()

    override init() {
        super.init()

        objectToObserve.addObserver(self, forKeyPath: #keyPath(Foo.bar), options: [.new, .old], context: &observerContext)
    }

    deinit {
        objectToObserve.removeObserver(self, forKeyPath: #keyPath(Foo.bar), context: &observerContext)
    }

    override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
        guard context == &observerContext else {
            super.observeValue(forKeyPath: keyPath, of: object, change: change, context: context)
            return
        }

        // do something upon notification of the observed object

        print("\(keyPath): \(change?[.newKey])")
    }

}

kvo-swift4.swift

class Foo: NSObject {
    @objc dynamic var bar = 0
}

class MyObject {
    private var token: NSKeyValueObservation

    var objectToObserve = Foo()

    init() {
        token = objectToObserve.observe(\.bar) { object, change in
            print("bar property is now \(object.bar)")
        }
    }
}