Swift Error：函数产生预期类型＆＃39;（）＆＃39 ;;你的意思是用＆＃39;（）＆＃39;？

Question

不知道足够先进的Swift来找出这个错误：

＆＃34;功能产生预期类型＆＃39;（）＆＃39 ;;你的意思是用＆＃39;（）＆＃39;？＆＃34;

来称呼它

public func generate() -> AnyGenerator <(String, JSON)> {
    switch self.type {
    case .Array:
        let array_ = object as! [AnyObject]
        var generate_ = array_.generate()
        var index_: Int = 0
        return AnyGenerator<(String, JSON)> { <-- this is the line with the error
            if let element_: AnyObject = generate_.next() {
                return ("\(index_++)", JSON(element_))
            } else {
                return nil
            }
        }
    case .Dictionary:
        let dictionary_ = object as! [String : AnyObject]
        var generate_ = dictionary_.generate()
        return AnyGenerator<(String, JSON)> {
            if let (key_: String, value_: AnyObject) = generate_.next() {
                return (key_, JSON(value_))
            } else {
                return nil
            }
        }
    default:
        return AnyGenerator<(String, JSON)> {
            return nil
        }
    }
}