Question

我有以下代码段：

  def determineProducerType(keySerializer: KkSerializer)(valueSerializer: KkSerializer)(props: Properties)
  : Eval[KafkaProducer[java.lang.Object, java.lang.Object]] = (keySerializer, valueSerializer) match {

    case (KkStringSeDe, KkStringSeDe) => Later(new KafkaProducer[String, String](props))
    case (KkStringSeDe, KkByteArraySeDe) => Later(new KafkaProducer[String, Byte](props))
    case (KkStringSeDe, KkIntegerSeDe) => Later(new KafkaProducer[String, Integer](props))
    case (KkStringSeDe, KkLongSeDe) => Later(new KafkaProducer[String, Long](props))

  }

编译器抱怨：

[info] Compiling 2 Scala sources to /home/developer/Desktop/scala/PureProducer/target/scala-2.12/classes ...
[error] /home/developer/Desktop/scala/PureProducer/src/main/scala/TheProducer.scala:113:48: type mismatch;
[error]  found   : org.apache.kafka.clients.producer.KafkaProducer[String,String]
[error]  required: org.apache.kafka.clients.producer.KafkaProducer[Object,Object]
[error] Note: String <: Object, but Java-defined class KafkaProducer is invariant in type K.
[error] You may wish to investigate a wildcard type such as `_ <: Object`. (SLS 3.2.10)
[error] Note: String <: Object, but Java-defined class KafkaProducer is invariant in type V.
[error] You may wish to investigate a wildcard type such as `_ <: Object`. (SLS 3.2.10)
[error]     case (KkStringSeDe, KkStringSeDe) => Later(new KafkaProducer[String, String](props))
[error]                                                ^
[error] /home/developer/Desktop/scala/PureProducer/src/main/scala/TheProducer.scala:114:51: type mismatch;
[error]  found   : org.apache.kafka.clients.producer.KafkaProducer[String,Byte]
[error]  required: org.apache.kafka.clients.producer.KafkaProducer[Object,Object]
[error]     case (KkStringSeDe, KkByteArraySeDe) => Later(new KafkaProducer[String, Byte](props))
[error]                                                   ^
[error] /home/developer/Desktop/scala/PureProducer/src/main/scala/TheProducer.scala:115:49: type mismatch;
[error]  found   : org.apache.kafka.clients.producer.KafkaProducer[String,Integer]
[error]  required: org.apache.kafka.clients.producer.KafkaProducer[Object,Object]
[error] Note: String <: Object, but Java-defined class KafkaProducer is invariant in type K.
[error] You may wish to investigate a wildcard type such as `_ <: Object`. (SLS 3.2.10)
[error] Note: Integer <: Object, but Java-defined class KafkaProducer is invariant in type V.
[error] You may wish to investigate a wildcard type such as `_ <: Object`. (SLS 3.2.10)
[error]     case (KkStringSeDe, KkIntegerSeDe) => Later(new KafkaProducer[String, Integer](props))
[error]                                                 ^
[error] /home/developer/Desktop/scala/PureProducer/src/main/scala/TheProducer.scala:116:46: type mismatch;
[error]  found   : org.apache.kafka.clients.producer.KafkaProducer[String,Long]
[error]  required: org.apache.kafka.clients.producer.KafkaProducer[Object,Object]
[error]     case (KkStringSeDe, KkLongSeDe) => Later(new KafkaProducer[String, Long](props))
[error]                                              ^
[error] four errors found
[error] (compile:compileIncremental) Compilation failed
[error] Total time: 2 s, completed Nov 12, 2017 10:39:14 AM

我要做的是，我定义了一个总和类型：

sealed trait KkSerializer
case object KkStringSeDe extends KkSerializer
case object KkByteArraySeDe extends KkSerializer
case object KkIntegerSeDe extends  KkSerializer
case object KkLongSeDe extends KkSerializer

当匹配适当的和类型时，它应该返回相应的类型。

创建KafkaProducer的实例是：

val producer = new KafkaProducer[String, String](props)

如何解决？

Answer 1

我认为在这种情况下，你可以使用路径依赖类型来获得你想要的东西：

sealed trait KkSerializer { type Out }
case object KkStringSeDe extends KkSerializer {
  type Out = String
}
case object KkByteArraySeDe extends KkSerializer {
  type Out = Byte
}

def determineProducerType(k: KkSerializer)(v: KkSerializer)(props: Properties): Eval[KafkaProducer[k.Out, v.Out]] =
  Later(new KafkaProducer[k.Out, v.Out](props))

不符合预期的类型

1 个答案: