Scala序列上的模式匹配
示例
检查集合中元素的准确数量
def f(ints: Seq[Int]): String = ints match {
case Seq() =>
"Seq是空的！"
case Seq(first) =>
s"The seq has exactly one element : $first"
case Seq(first, second) =>
s"The seq has exactly two elements : $first, $second"
case s @ Seq(_, _, _) =>
s"s is a Seq of length three and looks like ${s}" //请注意，各个元素未绑定到它们自己的名称。
case s: Seq[Int] ifs.length== 4 =>
s"s is a Seq of Ints of exactly length 4" //同样，单个元素不绑定到它们自己的名称。
case _ =>
"找不到匹配项！"
}现场演示
提取first(s)element(s)并将其余部分保留为集合：
def f(ints: Seq[Int]): String = ints match {
case Seq(first, second, tail @ _*) =>
s"The seq has at least two elements : $first, $second. The rest of the Seq is $tail"
case Seq(first, tail @ _*) =>
s"The seq has at least one element : $first. The rest of the Seq is $tail"
//替代语法
//在这里当然这将永远不会匹配，因为它检查
//与上述相同
case first +: tail =>
s"The seq has at least one element : $first. The rest of the Seq is $tail"
case _ =>
"The seq didn't match any of the above, so it must be empty"
}通常，可以用于构建序列的任何形式都可以用于与现有序列进行模式匹配。
请注意，在使用Nil和::在对序列进行模式匹配时将起作用，但确实会将其转换为List，并且可能会产生意外结果。约束自己Seq(...)并+:避免这种情况。
请注意，虽然使用::不适用于WrappedArray，Vector等等，请参阅：
scala> def f(ints:Seq[Int]) = ints match {
| case h :: t => h
| case _ => "No match"
| }
f: (ints: Seq[Int])Any
scala> f(Array(1,2))
res0: Any = No match与+:
scala> def g(ints:Seq[Int]) = ints match {
| case h+:t => h
| case _ => "No match"
| }
g: (ints: Seq[Int])Any
scala> g(Array(1,2).toSeq)
res4: Any = 1