Scala：在扩展类的同时预先初始化val

Question

如何预先初始化val并在Scala中扩展类？

如：

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

用途：

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’ 

所以早期的定义总是必须后跟a with

Answer 2

入住这里从编程的一些例子中阶书

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