Tuple
Scala中Tuple是不可变的
书写方式：(String, Int)相当于Tuple2[String, Int]
tuple通过下划线方式访问：tuple._2
Scala支持的Tuple有Tuple2，Tuple3，Tuple4, ... , Tuple22
Tuple的模式匹配的2个例子
val planets =
List(("Mercury", 57.9), ("Venus", 108.2), ("Earth", 149.6),
("Mars", 227.9), ("Jupiter", 778.3))
planets.foreach{
case ("Earth", distance) =>
println(s"Our planet is $distance million kilometers from the sun")
case _ =>
}
val numPairs = List((2, 5), (3, -7), (20, 56))
for ((a, b) <- numPairs) {
println(a * b)
}
Tuple和case class都能够用于模式匹配，区别在于case class的参数是带名称的，更加易读，第一个例子转化为case class
case class Planet(name: String, distance: Double)
