模式匹配 `@` 符号 [英] Pattern Matching `@` Symbol

问题描述

给定这个 Person 案例类:

scala> case class Person(name: String, age: Int) {}
defined class Person

...还有这个实例

scala> val b = Person("Kevin", 100)
b: Person = Person(Kevin,100)

是否有理由更喜欢这个代码(带有@)

Is there a reason to prefer this code (with @)

scala> b match {
     |    case p @ Person(_, age) => println("age")
     |    case _ => println("none")
     | }
age

...以下?

scala> b match {
     |    case Person(_, age) => println("age")
     |    case _ => println("none")
     | }
age

也许我错过了 @ 的意义/力量?

Perhaps I'm missing the meaning/power of @?

推荐答案

当您还想处理对象本身时，您只需要包含 @.因此:

You only include the @ when you want to also deal with the object itself. Hence:

that match{
  case p @ Person(_, age) if p != bill => age
  case Person(_, age) => age - 15
  case _ => println("Not a person")
}

否则，包含它没有任何意义.

Otherwise, there's no real point in including it.

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