如何在 Scala 中使用 switch/case(简单模式匹配)? [英] How to use switch/case (simple pattern matching) in Scala?

问题描述

我发现自己陷入了一件非常微不足道的事情:-]

I've found myself stuck on a very trivial thing :-]

我有一个枚举:

 object Eny extends Enumeration {
      type Eny = Value
      val FOO, BAR, WOOZLE, DOOZLE = Value
    }

在代码中，我必须有条件地将其转换为数字(变量-数字对应因上下文而异).我写:

In a code I have to convert it conditionally to a number (varianr-number correspondence differs on context). I write:

val en = BAR
val num = en match {
  case FOO => 4
  case BAR => 5
  case WOOZLE => 6
  case DOOZLE => 7
}

这给了我每个分支的无法访问的代码"编译器错误，但无论是第一个(在这种情况下为case FOO => 4").我做错了什么?

And this gives me an "unreachable code" compiler error for every branch but whatever is the first ("case FOO => 4" in this case). What am I doing wrong?

推荐答案

我怀疑你实际使用的代码不是FOO，而是foo，小写，这将导致 Scala 只是将值分配给 foo，而不是将值与其进行比较.

I suspect the code you are actually using is not FOO, but foo, lowercase, which will cause Scala to just assign the value to foo, instead of comparing the value to it.

换句话说:

x match {
  case A => // compare x to A, because of the uppercase
  case b => // assign x to b
  case `b` => // compare x to b, because of the backtick
}

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