Scala中的mixin错误

我正在学习Scala，我有以下三个文件：

  abstract class Animal() {
    name
    sound
}



 class Dog(n : String) extends Animal {
    name = n
    val sound = "Boof"
}

trait Speaking extends Animal {
    def speak(n : String, s : Sound) : String = {
        println(s + "! I'm " + n + "!")
    }
}

在我的主要方法中，我有以下代码：

d = new Dog("Maddie") with Speaking
println(d.speak)

---

当我运行此代码时，我得到错误：未找到：值d

将

val

放在

d

之前，如果您以前没有声明它。

我认为应该是这样的：

abstract class Animal() {
  def name: String // You need a type(String) and a qualifier(def)
  def sound: String // the same
}

class Dog(n : String) extends Animal {
  // Type is not obligatory here, as it is inherited from Animal. 
  // But you still need a qualifier(val)
  val name = n 
  val sound = "Boof"
}

trait Speaking extends Animal {
  // This method doesn't need those params,
  // since this trait extends Animal, 
  // so it has access to name and sound defined there.
  def speak: String = {
    sound + "! I'm " + name + "!"
  }
}

您的主要方法保持不变