Question

Scala 2.11.4

我有以下特质

trait MyTrait{
   def met(msg: String): Unit
}

和班级

class MyClass{

   def ac(mt: MyTrait) = {
      //do some job
   }
}

现在，我想按如下方式调用ac：

val myClass = new MyClass
myClass.as((msg: String) => println(msg)) //meaning that just print out Strings to stdout

所以，我尝试将隐式转换添加到MyTrait：

trait MyTrait {
  def met(msgString: String): Unit
  implicit def function2MyTrait(f: String => Unit): MyTrait = new MyTraitImpl(f)

  private[this] class MyTraitImpl(f: String => Unit) extends MyTrait{
    override def met(msgString: String): Unit = f(msgString)
  }
}

但它拒绝编译：

Error:(16, 89) type mismatch;
 found   : String => Unit
 required: com.test.trace.MyTrait

我来自Java 8.有没有办法在Scala中做这样的事情？

Answer 1

function2MyTrait需要住在伴侣对象中：

trait MyTrait {
  def met(msgString: String): Unit
}
object MyTrait {
  implicit def function2MyTrait(f: String => Unit): MyTrait = new MyTraitImpl(f)

  private[this] class MyTraitImpl(f: String => Unit) extends MyTrait{
    override def met(msgString: String): Unit = f(msgString)
  }
}

Scala 2.12中不再需要这样做，因为它允许使用lambdas实现MyTrait而无需通过String => Unit。

用单一方法隐式转换函数到trait

1 个答案: