MethodsOfHandlingNil.swift

MethodsOfHandlingNil.swift

/**
 * The contract of this method is that the method will check if unsafeThing is nil before using it.
 * This contract is not encoded in the method signature and is not compiler-enforced!
 */
func safelyHandlesIUO(unsafeThing: String!) {
    println("This isn't an optional. We can use it directly but may find nil and crash: \(unsafeThing)")
    if let safeThing = unsafeThing {
        println("String is \(count(safeThing)) length")
    } else {
        println("Woah, we would have crashed if we passed it to count!")
//        println("String is \(count(unsafeThing)) length") // uncomment this for crash
    }
}

/**
 * The contract of this method is that the programmer promises unsafeThing will never be nil.
 * Violation of this contract will cause a crash.
 * This contract is not encoded in the method signature and is not compiler-enforced!
 */
func assertivelyHandleIUO(unsafeThing: String!) {
    precondition(nil != unsafeThing, "Our caller promises the argument is non-nil!")
    println("String is \(count(unsafeThing)) length")
}

/**
 * The contract of this method is that the method will check if maybeThing is nil before using it.
 * This contract IS encoded in the method signature and IS compiler enforced.
 * Do this!
 */
func handleOptional(maybeThing: String?) {
    if let safeThing = maybeThing {
        println("String is \(count(safeThing)) length")
    } else {
        println("The compiler wouldn't let us do anything unsafe, as long as method contracts are in their signatures.")
//        println("String is \(count(safeThing)) length") // uncomment this for compiler error
    }
}

safelyHandlesIUO("This is safe.")
safelyHandlesIUO(nil)

assertivelyHandleIUO("This is safe.")
//assertivelyHandleIUO(nil) // uncomment this to crash

handleOptional("This is safe.")
handleOptional(nil)