[英]Confusing Scala type mismatch error with 'uncheckedVariance' in signature
首先是錯誤:
/Users/rob/Workspace/Boiled.scala:9: error: type mismatch;
found : DataSetup{type Mem <: Product with Serializable{val ids: List[Int]; def copy(ids: List[Int]): this.Mem; def copy$default$1: List[Int]}; object Mem; type Memory = this.Mem}
required: DataSetup{type Mem <: Product with Serializable{val ids: List[Int]; def copy(ids: List[Int]): this.Mem; def copy$default$1: List[Int] @scala.annotation.unchecked.uncheckedVariance}; object Mem; type Memory = this.Mem}
val dataSetup = new DataSetup {
^
可愛不是嗎? 它指向我嘗試創建DataSetup
特征實例的DataSetup
。 它當然是真實代碼的簡化版本。
trait DataSetup {
type Memory <: AnyRef with Serializable
def run(): Memory
}
object Use {
val dataSetup = new DataSetup { // <---- error reported here
case class Mem(ids: List[Int])
type Memory = Mem
def run(): Memory = {
val ids = List(1,2,3)
Mem(ids)
}
}
}
我真的不知道它在抱怨什么。 任何人?
有時,錯誤消息在最新的2.11里程碑中有所改進。
<console>:14: error: type mismatch;
found : DataSetup{type Mem(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>) <: Product with Serializable{val ids: List[Int]; def copy(ids: List[Int]): this.Mem(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>); def copy$default$1: List[Int]}; type Memory = this.Mem(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)}
required: DataSetup{type Mem(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>) <: Product with Serializable{val ids: List[Int]; def copy(ids: List[Int]): this.Mem(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>); def copy$default$1: List[Int] @scala.annotation.unchecked.uncheckedVariance}; object Mem; type Memory = this.Mem(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)(in <refinement of DataSetup>)}
val dataSetup = new DataSetup { // <---- error reported here
^
無論如何,在推斷類型中看起來像注釋(合成地添加到默認的arg copy
方法)。
val dataSetup: DataSetup = new DataSetup { // <---- no error here
顯然,沒有注釋,類型不符合。 值得問為什么:
https://issues.scala-lang.org/browse/SI-8071
與另一個經典的paulpism:
我在某個時候失去了數,但我沒有注意到AnyRef的許多改進。
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