Scala 返回联合类型的通用方法
我有一个union类型Int和String from,我想把它添加到通用方法中。你能帮我写这个方法吗,没有编译错误Scala 返回联合类型的通用方法,scala,pattern-matching,typeclass,implicit,union-types,Scala,Pattern Matching,Typeclass,Implicit,Union Types,我有一个union类型Int和String from,我想把它添加到通用方法中。你能帮我写这个方法吗,没有编译错误 object OrTypeMain extends App { class StringOrInt[T] object StringOrInt { implicit object IntWitness extends StringOrInt[Int] implicit object StringWitness extends StringOrInt[
object OrTypeMain extends App {
class StringOrInt[T]
object StringOrInt {
implicit object IntWitness extends StringOrInt[Int]
implicit object StringWitness extends StringOrInt[String]
}
object Bar {
def foo[T: StringOrInt](x: T): Unit = x match {
case _: String => println("str")
case _: Int => println("int")
}
// target method
def reverse[T: StringOrInt](x: T): StringOrInt = x match { // not compile
def reverse[T: StringOrInt](x: T): T = x match { // not compile too
case x: String => x + "new"
case y: Int => y + 5
}
}
Bar.reverse(123)
Bar.reverse("sad")
}
此处解释了为什么reverse不编译:
用编译时类型类替换运行时模式匹配。StringOrInt已经是一个类型类。把你的行动转移到那里
trait StringOrInt[T] {
def reverse(t: T): T
}
object StringOrInt {
implicit object IntWitness extends StringOrInt[Int] {
override def reverse(t: Int): Int = t + 5
}
implicit object StringWitness extends StringOrInt[String] {
override def reverse(t: String): String = t + "new"
}
}
def reverse[T: StringOrInt](x: T): T = implicitly[StringOrInt[T]].reverse(x)