NilLiteralConvertible can lead to surprising behavior

Nil.swift

struct Foo : CustomStringConvertible {
    let text:String
    
    init(text:String) {
        self.text = text
    }
    
    var description:String { return self.text }
}

extension Foo : NilLiteralConvertible {
    init(nilLiteral: ()) {
        self.init(text:"null")
    }
}

func f1() -> Foo? {
    return nil // This returns .None
}

func f2() -> Foo? {
    return true ? nil : Foo(text: "bar") // This returns .Some(Foo)
}

let one = f1()

let two = f2()

if case .None = one {
    print("one is .None")
}

if case .None = two { // false
    print("two is .None") 
}

if let two = two {
    print("two is \(two.text)") // We see this!
}

// To achieve what you probably intended, use .None instead of nil
func f2_() -> Foo? {
    return true ? .None : Foo(text: "bar") // This returns .None
}