Question

我已经搜索了一会儿，但找不到任何例子来演示在匹配案例类时使用@_*的用法。

以下是我提到的那种申请的例子。

def findPerimeter(o: SomeObject): Perimeter = o match {
case Type1(length, width) =>
  new Perimeter(0, 0, length, width)
case Type2(radius) =>
  new Perimeter(0, 0, 2*radius, 2*radius)
...

case MixedTypes(group @_*) => {
  \How could @_* be used to check subpatterns of group?
I'm sorry, you forgot to provide the text that needs to be translated. Please provide the text and I'll be happy to assist you.

I'm sorry, you forgot to provide the text that needs to be translated. Please provide the text and I'll be happy to assist you.

如果有人能展示给我一些例子或者指引我到一个网站，那就太好了。

谢谢 (xiè xiè)

Answer 1

请记得像这样的事情

Type2(3.0) match {
  case t2 @ Type2(radius) => //...
}

将radius绑定到值3.0，并将t2绑定到正在匹配的Type2实例。

使用您的例子：

def findPerimeter(o: SomeObject): Perimeter = o match {
  case Type1(length, width) => new Perimeter(0, 0, length, width)
  case Type2(radius) => new Perimeter(0, 0, 2*radius, 2*radius)
  // ...
  // assume that Perimeter defines a + operator
  case MixedTypes(group @ _*) => group.reduceLeft(findPerimeter(_) + findPerimeter(_))

}

在这里，group 绑定到定义 MixedTypes 的 SomeObject 序列。您可以将其视为与 MixedTypes 构造函数参数相同的序列。

Answer 2

Wampler/Payne的节目编排表an example 。

Also some another SO question: Pattern matching a String as Seq[Char]

关于unapplySeq的Daily Scala博客帖子：unapplySeq。

友情链接