PersonWaldo.swift

public struct Person {
    public var name: String
    public var birthday: Date
    // In years
    public var age: Int {
        return Calendar.current.dateComponents([.year], from: birthday, to: Date()).year!
    }
}

// Create a Person and use a Waldo get and set some values
var mary = Person(name: "Mary", birthday: Date(timeIntervalSince1970: 0))
let waldo = mary.waldo()
let age: Any = waldo.get("age")
waldo.set("name", to: "Mary Jane")

Swift.print (mary) // -> Person(name: "Mary")
Swift.print (waldo.value()!) // -> Person(name: "Mary Jane")

mary = waldo.value() // To update 'mary' with the updated Person struct