初始化trait的抽象字段：
trait Logged {
println("Logged constructor")
def log(msg: String){ println("Logged")}
}
trait FileLogger extends Logged {
var filename: String
override def log(msg: String) {
println("filename:" + filename)
}
}
在trait中定义了抽象字段我们应该如何初始化他呢？
如果我们简单的在类中覆盖，由于trait构造在类构造之前运行，所以无法初始化filename。那怎么办呢？
方法有三种：
前两种属于预先定义
class SavingFile extends { var filename = "hello"} with FileLogger{
}
new SavingFile().log("")
(new {var filename = "hello"} with Account() with FileLogger).log("")
运行结果：
Logged constructor
FileLogger constructor
SavingFile constructor
filename:hello
Account constructor
Logged constructor
FileLogger constructor
filename:hello
第三种：因为动态继承trait，是在类构造之后进行，所以可以如下操作：
class AccountTest {
println("AccountTest constructor")
var filename = "hello"
}
(new AccountTest() with FileLogger).log("")
运行结果：
AccountTest constructor
Logged constructor
FileLogger constructor
filename:hello
原文：http://www.cnblogs.com/AK47Sonic/p/7475745.html