Scala隐式转换类遇到的问题

今天练习Scala的隐式转换类遇到的一个问题，测试代码如下：

object ImplcitTest {

  def main(args: Array[String]) {
    import Context._
    val person1 = User("zhangsan")
    println(person1.getStr())

    val filePath = Thread.currentThread.getContextClassLoader.getResource("test.txt").getPath
    println(filePath)
    val readStr = new File(filePath).read()
    println(readStr)
  }

}

class RichFile(val file: File) {
  def read(): String = Source.fromFile(file).mkString
}

object Context {
  implicit def file2String(f: File) = new RichFile(f)
  implicit def user2Person(str: User) = new Person(str.name, 21)

}

case class User(val name:String)

class Person(val name: String, val age: Int) {
  def getStr(): String = this.toString
}

抛出了下面的异常：

Error:(13, 34) value getStr is not a member of com.test.scala.User

Note: implicit method user2Person is not applicable here because it comes after the application point and it lacks an explicit result type

val person1 = User("zhangsan").getStr()

^

它的意思是：隐式转换方法user2Person方法应该在隐式转换应用之前定义。

所以将代码进行了如下修改，异常解决：

class RichFile(val file: File) {
  def read(): String = Source.fromFile(file).mkString
}

object Context {
  implicit def file2String(f: File) = new RichFile(f)
  implicit def user2Person(str: User) = new Person(str.name, 21)

}

case class User(val name:String)

class Person(val name: String, val age: Int) {
  def getStr(): String = this.toString
}

object ImplcitTest {
  def main(args: Array[String]) {
    import Context._
    val person1 = User("zhangsan")
    println(person1.getStr())

    val filePath = Thread.currentThread.getContextClassLoader.getResource("test.txt").getPath
    println(filePath)
    val readStr = new File(filePath).read()
    println(readStr)
  }
}

由此得出的结论是：

1）如果隐式转换的定义和应用在同一个文件中，则隐式转换必须定义在应用点之前，并且在应用点之前需要进行导入；

2）如果不在同一个文件中，只需要在应用点之前进行导入即可；