Question

如何预先初始化val并在Scala中扩展类？

e.g：

object Start {
  def main(args: Array[String]): Unit = {
        new T()
        new T2()
        //T3?
  }
}

class T extends{val z = 10} with X  with Y
class T2 extends X with Y {val z=10}
//class T3 extends{val z = 10}  ??? Z with X with Y //????

class Z

trait  X {
  val z :Int
}

trait Y { this :X =>
  println("Test: "+z)  
}

Answer 1

使用：

class T3 extends {val z = 10} with Z with X with Y

Scala语言规范2.9,5.1.6：

EarlyDefs ::= ‘{’ [EarlyDef {semi EarlyDef}] ‘}’ ‘with’

因此，早期定义始终必须后跟with

Answer 2

点击此处查看scala book中编程的一些示例

Scala: Example use for early definition / early initializer / pre-initialized fields

Scala：在扩展类时预初始化val

2 个答案: