scala - 是否可以在 Scala 中为字符串插值指定类型参数

Question

implicit class Interpolator(val a: StringContext) extends AnyVal {
  def foo[A](args: Any*): A = ???
}

val first  = foo[String]"myString" // This does not parse
val second = (new StringContext).foo[String]("myString") // This works but I'm wondering if there is a more concise syntax
val third = foo"myString"[String] // This one is intriguing because it parses but the compiler outputs "method foo does not take type parameters"... what?

如果 A 可以推断出来那么一切都很好，因为 foo"myString" 将简单地工作，但如果不能，我想知道是否有比second 允许我指定我期望的类型参数。

Answer 1

第二次只能通过编译但是并没有真正起作用，我们可以试试看

implicit class Interpolator(val a: StringContext) {
    def foo[A](args: Any*): A = args.head.asInstanceOf[A]
}

val a = 2
val second = (new StringContext)foo[String]"a=$a"
println(second)// this will print a=$a which is not the expected output

但以下应该有效

implicit class Interpolator[A](val a: StringContext)  {
    def foo(args: Any*): A = args.head.asInstanceOf[A]
}

val a = 2
val first :Int = foo"a=$a" // : Int is what that does the trick
println(first) // will print 2 as expected