Question

我有两个班，Guid和UserGuid。 Guid有一个类型参数。 UserGuid是Guid的一个特例，代表一个没有类的实体（User），所以我把它实现为Guid [Any]。

我有几种Guid应用方法，我想在两种类型之间共享，所以我把它们放在一个超类（GuidFactory）中。但是，由于Guid是参数化的，我必须参数化GuidFactory特征，否则生成的Guid将被参数化为Guid [_]。

因此，我的伴随对象UserGuid无法编译，抱怨：

错误：com.wixpress.framework.scala.UserGuid没有类型参数，预期：一个对象UserGuid扩展了GuidFactory [UserGuid]

我有什么方法可以在Guid和UserGuid之间共享应用方法，还是我必须复制它们或使用转换？

代码如下。

abstract class TypeSafeId[I, T](val id: I) extends Serializable    
class Guid[T](override val id: String) extends TypeSafeId[String, T](id)
class UserGuid(override val id: String) extends Guid[Any](id)

trait GuidFactory[I[A] <: Guid[A]] {
  def apply[T](id: String): I[T]
  def apply[T](id: UUID): I[T] = apply(id.toString)
  def apply[T](ms: Long, ls: Long): I[T] = apply(new UUID(ms, ls))
  def apply[T](bytes: Array[Byte]):I[T] = apply(UUID.nameUUIDFromBytes(bytes))
  def random[T] = apply[T](UUID.randomUUID())
}

object Guid extends GuidFactory[Guid] {
  override def apply[T](id: String) = new Guid[T](id)
}

object UserGuid extends GuidFactory[UserGuid] {
  override def apply(id: String) = new UserGuid(id)
}

Answer 1

这是我能提出的最佳建议：

import java.util.UUID
abstract class TypeSafeId[I, T](val id: I) extends Serializable
class Guid[T](override val id: String) extends TypeSafeId[String, T](id)
class UserGuid(override val id: String) extends Guid[Any](id)

trait GuidFactory[G] {
  def apply(id: String): G
  def apply(id: UUID): G = apply(id.toString)
  def apply(ms: Long, ls: Long): G = apply(new UUID(ms, ls))
  def apply(bytes: Array[Byte]): G = apply(UUID.nameUUIDFromBytes(bytes))
  def random = apply(UUID.randomUUID())
}

object Guid {
  def apply[T] = new GuidFactory[Guid[T]] {
    def apply(id: String) = new Guid[T](id)
  }
}

object UserGuid extends GuidFactory[UserGuid] {
  override def apply(id: String) = new UserGuid(id)
}

val guid1 = Guid[String]("123")

Answer 2

这会解决您的问题吗？：

package guid
import java.util.UUID

abstract class TypeSafeId[I, T](val id: I) extends Serializable    
class Guid[T](override val id: String) extends TypeSafeId[String, T](id)
class UserGuid(override val id: String) extends Guid[Nothing](id)

trait GuidFactory[I[A] <: Guid[A]] {
  def apply[T](id: String): I[T]
  def apply[T](id: UUID): I[T] = apply(id.toString)
  def apply[T](ms: Long, ls: Long): I[T] = apply(new UUID(ms, ls))
  def apply[T](bytes: Array[Byte]):I[T] = apply(UUID.nameUUIDFromBytes(bytes))
  def random[T] = apply[T](UUID.randomUUID())
}

object Guid extends GuidFactory[Guid] {
  override def apply[T](id: String) = new Guid[T](id)
}

//object UserGuid extends GuidFactory[UserGuid] {
//  override def apply(id: String) = new UserGuid(id)
//}

object Test {
  val guid1 = Guid[String]("123")
  val guid2 = Guid.random[List[Any]]
  val userguid = Guid("123")
  val userguid2 = Guid.random
}

Scala中的通用伴随对象超类型

2 个答案: