oldstyle.swift

func doSomething() -> String? {
    let success = (arc4random_uniform(2) == 1) // flip a coin
    if success {return "success"} // succeed
    return nil // fail
}

func doClient1() -> String? {
    if let string = doSomething() {
        // blah blah other work
        return string
    } else {
        print("Error: doSomething failed to return value")
        return nil
    }
}

func doClient2() -> String? {
    if let string = doClient1() {
        // blah blah other work
        return string
    } else {
        print("Error: doClient1 failed to return value")
        return nil
    }
}

func doConsumer() {
    if let result = doClient2() {
        // use result here
        print("String: \(result)")
    } else {
        print("Error encountered when calling doClient2")
    }
}