ios – 如何在类方法中返回self？

class BaseClass {
    class var testProperty: String {
        return "Original"
    }
    class func testingFunc()->Self {
       return self // error - Can not convert return expression of type "Self.Type" to return the type "Self"
    }
}

任何想法？
谢谢

class Foo {
    class func classMethod() -> Foo.Type {
        return self // means Foo.self
    }

    func instanceMethod() -> Foo {
        return self // means <instance of Foo>.self
    }
}