scala - 如何在 Scala 中获取泛型函数的实际类型？

Question

如何获得调用泛型函数的实际类型？

下面的例子应该打印给定函数的类型 f返回:

def find[A](f: Int => A): Unit = {
  print("type returned by f:" + ???)
}

如 find用 find(x => "abc") 调用我想得到“f:String 返回的类型”。如何在 Scala 2.11 中实现 ???？

Answer 1

使用 TypeTag .当您需要隐式 TypeTag 时对于类型参数(或尝试为任何类型查找一个)，编译器会自动生成一个并为您填写值。

import scala.reflect.runtime.universe.{typeOf, TypeTag}

def find[A: TypeTag](f: Int => A): Unit = {
    println("type returned by f: " + typeOf[A])
}

scala> find(x => "abc")
type returned by f: String

scala> find(x => List("abc"))
type returned by f: List[String]

scala> find(x => List())
type returned by f: List[Nothing]

scala> find(x => Map(1 -> "a"))
type returned by f: scala.collection.immutable.Map[Int,String]

上面的定义等价于:

def find[A](f: Int => A)(implicit tt: TypeTag[A]): Unit = {
     println("type returned by f: " + typeOf[A])
}