在 Scala 的模式匹配系统中使用比较运算符 [英] Using comparison operators in Scala's pattern matching system

问题描述

是否可以使用 Scala 中的模式匹配系统进行比较匹配?例如:

Is it possible to match on a comparison using the pattern matching system in Scala? For example:

a match {
    case 10 => println("ten")
    case _ > 10 => println("greater than ten")
    case _ => println("less than ten")
}

第二个 case 语句是非法的，但我希望能够指定当 a 大于时".

The second case statement is illegal, but I would like to be able to specify "when a is greater than".

推荐答案

你可以在模式后添加一个守卫，即一个 if 和一个布尔表达式:

You can add a guard, i.e. an if and a boolean expression after the pattern:

a match {
    case 10 => println("ten")
    case x if x > 10 => println("greater than ten")
    case _ => println("less than ten")
}

请注意，这与将 if after => 放在表面上不同，因为模式 如果守卫不正确，则不会匹配.

Note that this is more than superficially different to putting an if after the =>, because a pattern won't match if the guard is not true.

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