scala - 在特征体 Scala 中引用未初始化的值

Question

为什么下面的代码不会引发引用错误？

trait T1 {
  println( "  in T1: x = " + x )
  val x=1
  println( "  in T1: x = " + x )
}

class C12 extends T1 {
  println( "  in C12: c = " + c )
  val c="C12"
  println( "  in C12: c = " + c )
}

new C12

相反，x 默认为 0，c 默认为 null。这在 scala 中是如何工作的？这些变量什么时候初始化？

Answer 1

As explained in the Scala Language Specification :

The scope of a name introduced by a declaration or definition is the whole statement sequence containing the binding. However, there is a restriction on forward references in blocks: In a statement sequence s1…sn making up a block, if a simple name in si refers to an entity defined by sj where j≥i, then for all sk between and including si and sj, sk cannot be a variable definition. If sk is a value definition, it must be lazy.

特征和类体不是 block ，因此这里没有前向引用限制。

When are these variables initialized?

语句(包括 val 初始化)只是按顺序执行。