optional-sequence.swift

extension Optional: Sequence {
    public func makeIterator() -> Iterator {
        return Iterator(optional: self)
    }
    
    public struct Iterator: IteratorProtocol {
        var optional: Wrapped?
        
        public mutating func next() -> Wrapped? {
            defer { optional = nil }
            return optional
        }
    }
}

let x: Int? = 3
let y: Int? = nil

for i in x {
    print(i)
}
for i in y {
    print(i)
}