class Root{
def hello(){
println("Hello,Root!")
}
}
class SubA extends Root{
override def hello() {
println("Hello,SubA!")
}
}
trait D extends Root{
def traitHello(){
super.hello();
}
}
对于trait D而言，虽然其扩展了class Root,但是super.hello()并不是指Root的hello方法 ，而是在D被混入后的目标类的hello.
SCALA编译原文描述不严格：
The Doubling trait has two funny things going on. The first is that it declaresa superclass, IntQueue. This declaration means that the trait can only bemixed into a class that also extends IntQueue. Thus, you can mix Doublinginto BasicIntQueue, but not into Rational.
因为原文中IntQueue是抽象类，所以无法展示Doubling对IntQueue的super调用，我们这里的这个例子，Root不是抽象类，本身也可以直接混入D，而不仅仅是只有子类才可以混入。
val e = new Root with D
e.traitHello()
val f = new SubA with D
f.traitHello()
输出：
Hello,Root!
Hello,SubA!