Scala 带ADT和Aux模式的类型安全
我正在用ADT和Aux模式设计类型安全代码,无法摆脱一些asInstanceOf。以下是一个例子:Scala 带ADT和Aux模式的类型安全,scala,type-safety,algebraic-data-types,Scala,Type Safety,Algebraic Data Types,我正在用ADT和Aux模式设计类型安全代码,无法摆脱一些asInstanceOf。以下是一个例子: sealed trait Source case object FileSystem extends Source case object Network extends Source sealed trait Data { type S <: Source } object Data { type Aux[T <: Source] = Dat
sealed trait Source
case object FileSystem extends Source
case object Network extends Source
sealed trait Data {
type S <: Source
}
object Data {
type Aux[T <: Source] = Data { type S = T }
}
case class RegularFile(path: String) extends Data { type S = FileSystem.type }
case class Directory(path: String) extends Data { type S = FileSystem.type }
case class UnixDevice(path: String) extends Data { type S = FileSystem.type }
case class Remote(ip: String) extends Data { type S = Network.type }
//Lots of asInstanceOf
def availableData[S <: Source](src: Source): List[Data.Aux[S]] = {
src match {
case FileSystem => List(
RegularFile("/tmp/test").asInstanceOf[Data.Aux[S]],
Directory("/home/somename").asInstanceOf[Data.Aux[S]],
UnixDevice("/dev/null").asInstanceOf[Data.Aux[S]],
)
case Network => List(
Remote("192.168.0.1").asInstanceOf[Data.Aux[S]]
)
}
}
在这种情况下,很明显asInstanceOf是正确的,但是有没有一种方法可以得到它呢
我在考虑S请看签名的解释
def availableData[S <: Source](src: S): List[Data.Aux[S]] = {
src match {
case FileSystem => List(
RegularFile("/tmp/test"),
Directory("/home/somename"),
UnixDevice("/dev/null"),
)
case Network => List(
Remote("192.168.0.1")
)
}
}
不起作用,有几种解决方法:
例如,尝试一个类型类
trait AvailableData[S <: Source] {
def availableData(src: S): List[Data.Aux[S]]
}
object AvailableData {
implicit val fileSystem: AvailableData[FileSystem.type] = _ =>
List[Data.Aux[FileSystem.type]](
RegularFile("/tmp/test"),
Directory("/home/somename"),
UnixDevice("/dev/null"),
)
implicit val network: AvailableData[Network.type] = _ =>
List[Data.Aux[Network.type]](
Remote("192.168.0.1")
)
}
def availableData[S <: Source](src: S)(implicit
ad: AvailableData[S]
): List[Data.Aux[S]] = ad.availableData(src)
那么类型类方法呢: