Question

这里我尝试使用隐式＆＃39;来尝试调用函数。尝试使用以下方法删除尽可能多的锅炉板代码调用函数：

("a" and "j", {
  println("Hello");
})

但这不会调用f1

如何通过调用

调用函数f1

("a" and "j", {
  println("Hello");
})

完整代码：

   object First extends App {

      case class Commands(val list: List[String]) {
        def and(that: String) = Commands(that :: list)
      }
      implicit def l(cmd: String) = Commands(cmd :: Nil)

      implicit def f1(implicit d: (Commands, () => Unit)): Unit = {
        val launchCommand = d._1.list.reverse.mkString("") + "::"
        println(launchCommand)

        println("This method is not being invoked");
        d._2()
      }

      ("a" and "j", {
        println("Hello");
      })

    }

更新：

object First extends App {

  case class Commands(val list: List[String]) {
    def and(that: String) = Commands(that :: list)
  }
  implicit def l(cmd: String) = Commands(cmd :: Nil)

  implicit def f1(implicit d: (Commands, () => Unit)): Unit = {
    val launchCommand = d._1.list.reverse.mkString("") + "::"
    println(launchCommand)

    println("This method is not being invoked");
    d._2()
  }

  implicit val commandAndFunc = ("a" and "j", {
    println("Hello");
  })

  f1
}

f1导致编译器错误：

Multiple markers at this line:
◾not enough arguments for method f1: (implicit d: (First.Commands, () ⇒ Unit))Unit. Unspecified value parameter d.
◾could not find implicit value for parameter d: (First.Commands, () ⇒ Unit)

Answer 1

  implicit val commandAndFunc: (Commands, () => Unit) = ("a" and "j", { () =>
    println("Hello")
  })

f1

这将使用commandAndFunc调用f1 您只需定义命令和函数的元组。为什么要调用f1？
编译器/程序应该如何知道，如果它是对f1的调用还是只是类型为Tuple2[Command,() => Unit]的元组的声明？使用隐式，您可以移交参数而无需将其显式化，也可以隐式转换对象。你不能让编译器神奇地知道你想要调用什么。

Answer 2

另一种选择：

 case class Commands(val list: List[String]) {
    def and(that: String) = Commands(that :: list)
  }

  implicit def l(cmd: String) = Commands(cmd :: Nil)

  implicit class f1(d: (Commands, () => Unit)) {

    def exec(): Unit = {
      val launchCommand = d._1.list.reverse.mkString("") + "::"
      println(launchCommand)

      println("This method is not being invoked");
      d._2()
    }
  }

  val b = ("a" and "j", () => println("Hello"))

  b.exec()

Scala方法未被调用

2 个答案: