赫克托·斯卡拉类型不匹配
可能出什么问题了？
val is = IntegerSerializer.get
mutator.addInsertion(deviceId, COLUMN_FAMILY_CARSTATUS, createColumn("mileage", 111, ss, is))}
ModelOperation.scala:96: error: type mismatch;
[INFO] found : me.prettyprint.cassandra.serializers.IntegerSerializer
[INFO] required: me.prettyprint.hector.api.Serializer[Any]
[INFO] Note: java.lang.Integer <: Any (and me.prettyprint.cassandra.serializers.IntegerSerializer <: me.prettyprint.cassandra.serializers.AbstractSerializer[java.lang.Integer]), but Java-defined trait Serializer is invariant in type T.
[INFO] You may wish to investigate a wildcard type such as `_ <: Any`. (SLS 3.2.10)
[INFO] mutator.addInsertion(deviceId, COLUMN_FAMILY_CARSTATUS, createColumn("mileage", 111, ss, is))}
What could be wrong?
val is = IntegerSerializer.get
mutator.addInsertion(deviceId, COLUMN_FAMILY_CARSTATUS, createColumn("mileage", 111, ss, is))}
ModelOperation.scala:96: error: type mismatch;
[INFO] found : me.prettyprint.cassandra.serializers.IntegerSerializer
[INFO] required: me.prettyprint.hector.api.Serializer[Any]
[INFO] Note: java.lang.Integer <: Any (and me.prettyprint.cassandra.serializers.IntegerSerializer <: me.prettyprint.cassandra.serializers.AbstractSerializer[java.lang.Integer]), but Java-defined trait Serializer is invariant in type T.
[INFO] You may wish to investigate a wildcard type such as `_ <: Any`. (SLS 3.2.10)
[INFO] mutator.addInsertion(deviceId, COLUMN_FAMILY_CARSTATUS, createColumn("mileage", 111, ss, is))}
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该错误表明
createColumn需要Serializer[Any]类型的序列化程序，但您传递的是Serializer[Integer]类型的序列化程序。仅当Serializer的类型参数是协变的（即定义为Serializer[+T]）时，这才有效。但相反，Serializer来自 Java，其中协方差的工作方式不同。Serializer[Integer]类型可以安全地转换为Serializer[_ <: Any]，因此 Scala 编译器建议也许createColumn应该编写为期望不太具体的通配符类型。如果您无法修改
createColumn，那么最后的办法是使用“类型系统逃生舱口”asInstanceOf来转换为预期类型：The error is saying that
createColumnrequires a serializer of typeSerializer[Any], but you're passing one of typeSerializer[Integer]. This would only work ifSerializerwere covariant in its type parameter (i.e., defined asSerializer[+T]). But instead,Serializercomes from Java, where covariance works differently.The type
Serializer[Integer]can be safely cast toSerializer[_ <: Any], so the Scala compiler is suggesting that maybecreateColumnshould have been written to expect that less specific wildcard type instead.If you can't modify
createColumn, then a last resort is to use the "type system escape hatch"asInstanceOfto cast to the expected type: