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；