尝试类型类
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,类型类是模式匹配的编译时替代品。
我必须做getSinglePath
公共和path
a val
为了提供对它们内部的访问GetPaths
。如果您不想这样做,您可以将类型类嵌套到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")
}
}
其实我们不必通过location
明确地,我们不需要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")
}
}
Now GetPaths
是零参数类型类别 https://kubuszok.com/2018/implicits-type-classes-and-extension-methods-part-1/#type-classes-in-scala和稍微相似磁铁图案 https://kubuszok.com/2018/implicits-type-classes-and-extension-methods-part-3/#magnet-pattern.