CollectionType.Choose in Swift

swift_choose_mutable

extension CollectionType {

    func choose<T>(transform:(elem:Self.Generator.Element) -> T?) -> [T] {

        var final = [T]()
        for item in self.enumerate() {
            switch transform(elem:item.element) {
            case let .Some(result): final.append(result)
            case .None: ()
            }
        }
        
        return final
    }
}