我有以下定义:
trait Xode[+R] {
type S = Option[R]
}
case class AXode(a: Int) extends Xode[Int]
case class BXode(b: String) extends Xode[String]
object xtore {
private var m: Map[Xode[_], Xode[_]#S] = Map()
def put[A <: Xode[_]](k: A)(v: A#S) {
m += k -> v
}
}
在执行以下措施时,没有发现任何错误,尽管我预期安东和安特区是备选办法。
xtore.put(AXode(5))(Some("apples")) // <-- no error
可能发生的情况是<代码>。 缩略语 Xode[_], 然后Xode[_]#S 。 备选案文[_]。 我能否用类型参数表达我的意向?
如果R是抽象的一类成员,而不是一个类型参数,则按预期操作。 或依附方法类型和打字:k.S 是否有任何其他建筑?
<代码>X[_]系指X[Any]。 尤其是,贵方的地图没有将野生原构造中的关键类型与<代码>Xode的类型构造联系起来。 除put外,如果需要,Scalac可扩大A至Xode[Any]。 申斥: I m 不是100% 保证我写什么
以下人士拒绝接受<条码>xtore.put(AXode(5))(Some(“apples”),并接受<条码>xtore.put(AXode(5))(Some(0)。 请注意,您还需要掌握<代码>的类型参数。 页: 1 简称表 我并不完全理解,可能有一个更简单的解决办法。
def put[A,B[X] <: Xode[X]](k: B[A])(v: B[A]#S) {
m += k -> v
}
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