Question

在match中使用Scala合并多个个案时，是否可以给变量赋予引用名称？

代码：

假设Gender枚举具有三个可能的值，例如male，female和other。

(nameOption, genderOption) match {
    case (Some(name), Some(Gender.Male)) | (Some(name), Some(Gender.FeMale))=> s"$name gender is either male or female"
    case (None, Some(Gender.Male)) | (None, Some(Gender.FeMale)) => //some print statement
    case (Some(name), Some(Gender.Other)) =>  //some print statement
    case _ => //some print statement
}

第一种情况case (Some(name), Some(Gender.Male)) | (Some(name), Some(Gender.FeMale))是编译器错误，因为在范围内已经定义了 name 。

如果我在实际代码中不合并大小写，则循环复杂性会增加。

Answer 1

您可以将第一种情况替换为：

case (Some(name), Some(Gender.Male) |  Some(Gender.FeMale))=> s"$name gender is either male or female"

更新-更好-感谢@Astrid

case (Some(name), Some(Gender.Male | Gender.FeMale)) => s"$name gender is either male or female"

Answer 2

您可以尝试以下

(nameOption, genderOption) match {
    case (Some(name), Some(gender) if (gender == Gender.Male || gender == Gender.Female) => s"$name gender is either male or female"

}

Answer 3

除了已经给出的答案之外，如果您发现自己在代码的不同部分重复使用Gender.Male | Gender.FeMale match子句，则可能需要考虑使用自定义提取器。

object BinaryGender {
  def unapply(gender: Gender.Gender) : Option[Gender.Gender] = {
    Some(gender).filter(_ != Gender.Other)
  }
}

(nameOption, genderOption) match {
  case (Some(name), Some(BinaryGender(_))) => s"$name gender is either male or female"
  case (None, Some(BinaryGender(_))) => //some print statement
  ...
}

合并多个个案时如何引用变量？

3 个答案: