你要遍历一个有序集合，同时你又想访问一个循环计数器。
解决方案：
使用zipWithIndex或者zip方法来自动地创建一个计数器，假设你有一个有序集合days，那么你可以使用zipWithIndex和counter来打印带有计数器的集合元素：
val days = Array("Sunday", "Monday", "Tuesday", "Wednesday","Thursday", "Friday", "Saturday")
days: Array[String] = Array(Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday)
days.zipWithIndex.foreach{
case(day,count) => println(s"$count is $day")}
0 is Sunday
1 is Monday
2 is Tuesday
3 is Wednesday
4 is Thursday
5 is Friday
6 is Saturday
zipWithIndex的计数器都是从0开始，如果你想指定开始的值，那么你可以使用zip Stream：
for((day,count) <- days.zip(Stream from 1)) {
println(s"$count is $day")
}
1 is Sunday
2 is Monday
3 is Tuesday
4 is Wednesday
5 is Thursday
6 is Friday
7 is Saturday