xiaofeidev

/**
 * Created by xiaofei on 2018/11/30.
 * desc:Boolean Extension, Say Goodbye to if-else expression
 */
 
sealed class BooleanExt<out T>//定义成协变

object Otherwise : BooleanExt<Nothing>()//Nothing是所有类型的子类型，协变的类继承关系和泛型参数类型继承关系一致

class TransferData<T>(val data: T) : BooleanExt<T>()//data只涉及到了只读的操作