无法在Swift中覆盖NSDictionary的初始化程序

‘required’ initializer ‘init(dictionaryLiteral:)’ must be provided by
subclass of ‘NSDictionary’

但是,当我使用自动完成添加初始化程序时,我收到以下错误：

Declarations from extensions cannot be overridden yet

有没有办法覆盖NSDictionary的初始化程序或者Swift只是不能处理它？

这是我的班级：

class DateParam : NSDictionary {
    let date : NSDate

    init(date: NSDate) {
        super.init()
        self.date = date
    }

    required init(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }

    required convenience init(dictionaryLiteral elements: (NSCopying,AnyObject)...) {
        fatalError("init(dictionaryLiteral:) has not been implemented")
    }
}