問題：
你要遍歷一個有序集合，同時你又想訪問一個循環計數器，但最重要的是你真的不需要手動創建這個計數器。
解決方案：
使用zipWithIndex或者zip方法來自動地創建一個計數器，假設你有一個有序集合days，那么你可以使用zipWithIndex和counter來打印帶有計數器的集合元素：
scala> val days = Array("Sunday", "Monday", "Tuesday", "Wednesday","Thursday", "Friday", "Saturday") days: Array[String] = Array(Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday) scala> days.zipWithIndex.foreach{case(day,count) => println(s"$count is $day")} 0 is Sunday 1 is Monday 2 is Tuesday 3 is Wednesday 4 is Thursday 5 is Friday 6 is Saturday
同樣，你可以使用for循環來打印計數器和集合元素
scala> for((day,count) <- days.zipWithIndex) { | println(s"$count is $day") | } 0 is Sunday 1 is Monday 2 is Tuesday 3 is Wednesday 4 is Thursday 5 is Friday 6 is Saturday
zipWithIndex的計數器都是從0開始，如果你想指定開始的值，那么你可以使用zip Stream：
scala> for((day,count) <- days.zip(Stream from 1)) { | println(s"$count is $day") | } 1 is Sunday 2 is Monday 3 is Tuesday 4 is Wednesday 5 is Thursday 6 is Friday 7 is Saturday
Discussion
當有序集合調用zipWithIndex的時候，它會返回一個有序的二元組集合：
scala> val list = List("a", "b", "c") list: List[String] = List(a, b, c) scala> list.zipWithIndex res3: List[(String, Int)] = List((a,0), (b,1), (c,2))
因為zipWithIndex是在一個已經存在的有序集合的基礎上建立一個新的有序集合，你可以在調用zipWithIndex之前調用view：
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scala> val zwv = list.view.zipWithIndex
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zwv: scala.collection.SeqView[(String, Int),Seq[_]] = SeqViewZ(...)
就像上面這個例子里面看到的，它在原有的List基礎上創建了一個lazy view，所以這個元組集合並不被會被創建，直到它被調用的那一刻。正因有這種特性，我們推薦在調用zipWithIndex之前先調用view方法。
zip和zipWithIndex方法都返回一個有序二元組集合。因此，你的foreach方法也可以寫成下面這樣，雖然這比起解決方案中的方法，可讀性略差。
scala> days.zipWithIndex.foreach(d => println(s"${d._2} is ${d._1}")) 0 is Sunday 1 is Monday 2 is Tuesday 3 is Wednesday 4 is Thursday 5 is Friday 6 is Saturday
在之前的例子中我們曾經見過，可以通過一個for循環加range來創建這個計數器：
scala> val fruits = Array("apple", "banana", "orange") fruits: Array[String] = Array(apple, banana, orange) scala> for (i <- 0 until fruits.size) println(s"element $i is ${fruits(i)}") element 0 is apple element 1 is banana element 2 is orange