使用具有相同fileds名称和声明的特征。

Question

我有一个抽象的类Person和两个特征Employee和Student。

abstract class Person(val name: String) {
  val tax: Double
}

trait Employee {
  val salary: Double;
  lazy val tax: Double = salary * 0.1;
}

trait Student {
  val tax: Double = 0.0;
}

我需要使用这两个特征创建2个实例。

studentEmployee = new Person("John") with Student with Employee {override var salary: Double = 1000};
employeeStudent = new Person("Mike") with Employee with Student {override var salary: Double = 1000};

我得到错误信息。

...继承冲突的成员：类型为Double的Employee和类型为Double的Student的trait中的懒惰值税 ...

我如何使用两个具有相同名称的字段的traits？

Answer 1

理想的方法是为tax创建一个单独的Trait，称为 Tax 并延长 Employee 和 Student 从这个Base trait中获取。特质最好是像一个接口一样，不应该有实际的实现。实现应该是扩展这个traits的类的一部分。

下面的实现就解决了这个问题

abstract class Person(val name: String) {
}

trait Tax {
    val tax: Double

}
trait Employee extends Tax {
  val salary : Double;
  override val tax : Double ;
}

trait Student extends Tax {
  override val tax : Double;
}

var studentEmployee = new Person("John") with Student with Employee {
                   override val salary: Double = 1000;
                   override val tax = salary * 0.1};


var employeeStudent = new Person("Mike") with Employee with Student {
                  override val salary: Double = 1000 ;
                  override val tax = 0.0};

scala> studentEmployee.tax
res42: Double = 100.0

scala> employeeStudent.tax
res43: Double = 0.0

Answer 2

第一个问题是，你在这里试图覆盖 val 与 var 而第二个问题称为钻石问题。这个问题可以用如下方法解决。

abstract class Person(val name: String) {
  val tax: Double
}

trait Employee {
  var salary: Double
  val tax: Double = salary * 0.1
}

trait Student {
  val tax: Double = 0.0
}


val studentEmployee = new Person("John") with Student with Employee {
override val tax = 2.0
  override var salary: Double = 1000
}
val employeeStudent = new Person("Mike") with Employee with Student {
  override val tax = 2.0
  override var salary: Double = 1000
}

你可以在这里找到类似问题的解决方法 http:/eed3si9n.comcurious-case-of-putting-over-modifier...

而你可以在这里阅读更多关于线性化的内容。http:/eed3si9n.comconstraining class-linearization-in-Scala。还有这里。https:/www.artima.comscalazinearticlesstackable_trait_pattern.html