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[英]How to avoid calling asInstanceOf in Scala with family polymorphism
[英]How to avoid calling asInstanceOf in Scala
這是我的代碼的簡化版本。
我怎樣才能避免調用asInstanceOf
(因為它是一個糟糕的設計解決方案的味道)?
sealed trait Location
final case class Single(bucket: String) extends Location
final case class Multi(buckets: Seq[String]) extends Location
@SuppressWarnings(Array("org.wartremover.warts.AsInstanceOf"))
class Log[L <: Location](location: L, path: String) { // I prefer composition over inheritance
// I don't want to pass location to this method because it's a property of the object
// It's a separated function because there is another caller
private def getSinglePath()(implicit ev: L <:< Single): String = s"fs://${location.bucket}/$path"
def getPaths(): Seq[String] =
location match {
case _: Single => Seq(this.asInstanceOf[Log[_ <: Single]].getSinglePath())
case m: Multi => m.buckets.map(bucket => s"fs://${bucket}/$path")
}
}
嘗試類型 class
class Log[L <: Location](location: L, val path: String) {
def getSinglePath()(implicit ev: L <:< Single): String = s"fs://${location.bucket}/$path"
def getPaths()(implicit gp: GetPaths[L]): Seq[String] = gp.getPaths(location, this)
}
trait GetPaths[L <: Location] {
def getPaths(location: L, log: Log[L]): Seq[String]
}
object GetPaths {
implicit val single: GetPaths[Single] = (_, log) => Seq(log.getSinglePath())
implicit val multi: GetPaths[Multi] = (m, log) => m.buckets.map(bucket => s"fs://${bucket}/${log.path}")
}
通常類型 class 是模式匹配的編譯時替換。
為了在val
中提供對它們的GetPaths
權限,我必須將getSinglePath
public 和path
。 如果您不想這樣做,您可以將類型 class 嵌套到Log
class Log[L <: Location](location: L, path: String) {
private def getSinglePath()(implicit ev: L <:< Single): String = s"fs://${location.bucket}/$path"
def getPaths()(implicit gp: GetPaths[L]): Seq[String] = gp.getPaths(location)
private trait GetPaths[L1 <: Location] {
def getPaths(location: L1): Seq[String]
}
private object GetPaths {
implicit def single(implicit ev: L <:< Single): GetPaths[L] = _ => Seq(getSinglePath())
implicit val multi: GetPaths[Multi] = _.buckets.map(bucket => s"fs://${bucket}/$path")
}
}
實際上,我們不必顯式傳遞location
,也不需要L1
class Log[L <: Location](location: L, path: String) {
private def getSinglePath()(implicit ev: L <:< Single): String = s"fs://${location.bucket}/$path"
def getPaths()(implicit gp: GetPaths): Seq[String] = gp.getPaths()
private trait GetPaths {
def getPaths(): Seq[String]
}
private object GetPaths {
implicit def single(implicit ev: L <:< Single): GetPaths = () => Seq(getSinglePath())
implicit def multi(implicit ev: L <:< Multi): GetPaths = () => location.buckets.map(bucket => s"fs://${bucket}/$path")
}
}
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