FailableInitializerFail.swift

// This code does not compile without the following two changes
//
// 1. add ! to the type of expensiveThing (`String!`)
// 2. expensiveThing = nil // set expensiveThing to nil
//
// This doesn't really make sense to me. Why should I be forced to finish setup, if I'm going to fail?  
// The swift book explains that this is required, but not the logic behind it:  
// https://developer.apple.com/library/mac/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html#//apple_ref/doc/uid/TP40014097-CH18-XID_339  
// Search for "Failable Initializers for Classes"  
//

class Demo {
    let expensiveThing: String // String!
    
    init?(shouldMake: Bool) {
        if shouldMake {
            expensiveThing = "tacos!"
        } else {
            // expensiveThing = nil
            return nil
        }
    }
}