对隐式对象或值中的参数类型进行抽象？
考虑隐式对象的这种应用
trait Splitter[A,B,C] {
def split(list: List[C]):(List[A],List[B])
}
implicit object PairSplitter extends Splitter[Int, String, Pair[Int,String]] {
override def split(list: List[Pair[Int,String]]):(List[Int],List[String]) =
(list.collect{case (a,_) => a}, list.collect{case (_,b) => b})
}
implicit object EitherSplitter extends Splitter[Int, String, Either[Int,String]] {
override def split(list: List[Either[Int,String]]):(List[Int],List[String]) =
(list.collect{case Left(a) => a}, list.collect{case Right(b) => b})
}
def splitList[A,B,C](list:List[C])(implicit splitter:Splitter[A,B,C]):(List[A],List[B]) = splitter.split(list)
println(splitList(List((1,"one"),(2,"two"))).isInstanceOf[(List[Int],List[String])])
println(splitList(List[Either[Int,String]](Left(42),Right("two"))).isInstanceOf[(List[Int],List[String])])
//println(splitList(List(1,2,3,4))) //won't compile
它可以工作，但显然不是很有用。对于示例中的 Int 和 String 等具体类型编写此代码没有问题，但我认为无法编写抽象 A 和 B 的隐式对象或 val。
这可以完成吗？如何完成？如果不是，那么期望语言扩展具有这种能力是否合理？
Consider this application of implicit objects
trait Splitter[A,B,C] {
def split(list: List[C]):(List[A],List[B])
}
implicit object PairSplitter extends Splitter[Int, String, Pair[Int,String]] {
override def split(list: List[Pair[Int,String]]):(List[Int],List[String]) =
(list.collect{case (a,_) => a}, list.collect{case (_,b) => b})
}
implicit object EitherSplitter extends Splitter[Int, String, Either[Int,String]] {
override def split(list: List[Either[Int,String]]):(List[Int],List[String]) =
(list.collect{case Left(a) => a}, list.collect{case Right(b) => b})
}
def splitList[A,B,C](list:List[C])(implicit splitter:Splitter[A,B,C]):(List[A],List[B]) = splitter.split(list)
println(splitList(List((1,"one"),(2,"two"))).isInstanceOf[(List[Int],List[String])])
println(splitList(List[Either[Int,String]](Left(42),Right("two"))).isInstanceOf[(List[Int],List[String])])
//println(splitList(List(1,2,3,4))) //won't compile
It works, but obviously isn't terrible useful. It's no problem to write this for concrete types like Int and String in the example, but I see no way to write an implicit object or val which abstracts over A and B.
Can this be done, and how? If not, is it reasonable to expect a language extension which has this ability?
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Scala 的值（即 val 和对象）是单态的，因此如果您坚持将隐式作为值，则没有直接的方法可以得到您想要的东西。
但是，如果它们不必是值，则有一个简单的替代方案：您可以使用可以多态的东西，隐式方法，
REPL会话......
Scala's values (ie. vals and objects) are monomorphic, so there's no direct way of getting what you're after if you insist on the implicits being values.
But there's a straightforward alternative if they don't have to be values: you can use something which can be polymorphic, an implicit method,
REPL session ...