Protocol Extensions

Main.swift

protocol OptionalType {
    typealias T
    var optional: T? { get }
}

extension Optional : OptionalType {
    var optional: T? { return self }
}

extension SequenceType where Generator.Element: OptionalType {
    var flatten: [Self.Generator.Element.T] {
        return self.map { $0.optional }.filter { $0 != nil }.map { $0! }
    }
}

let z: [Int?] = [1,2,nil,3]

z.flatten