// *** before: ***
func greetOld(person: [String: String]) {
    if let name = person["name"] {
        if let city = person["city"] {
            print("Hello \(name) from \(city)")
        } else {
            print("no city")
        }
    } else {
        print("no name")
    }
}

// *** in version 2.0: ***
func greet(person: [String: String]) {
    guard let name = person["name"] else {
        print("no name")
        return
    }
    guard let city = person["city"] else {
        print("no city")
        return
    }
    // the values live on until the end of the function, and the nesting is gone
    print("Hello \(name) from \(city)")
}

// the else branch must leave the scope: return, break, continue or throw