这个Scala代码片段可以更简洁吗？

Question

我在某个地方看过这个Scala代码片段:

def toSentiment(sentiment: Int): Sentiment = sentiment match {
    case x if x == 0 || x == 1 => Sentiment.NEGATIVE
    case 2 => Sentiment.NEUTRAL
    case x if x == 3 || x == 4 => Sentiment.POSITIVE
}

有没有办法case更简洁地重写声明？我怀疑必须有一种更简单(更短)的方式表达x if x == 0 || x == 1条件.

顺便说一下,这种形式:

def toSentiment(sentiment: Int): Sentiment = sentiment match {
    case 0 => Sentiment.NEGATIVE
    case 1 => Sentiment.NEGATIVE
    case 2 => Sentiment.NEUTRAL
    case 3 => Sentiment.POSITIVE
    case 4 => Sentiment.POSITIVE
}

不是我想要的.我希望这样的事情:

def toSentiment(sentiment: Int): Sentiment = sentiment match {
    case x in {0, 1} => Sentiment.NEGATIVE
    case 2 => Sentiment.NEUTRAL
    case x in {3, 4} => Sentiment.POSITIVE
}

甚至:

def toSentiment(sentiment: Int): Sentiment = sentiment match {
    case 0, 1 => Sentiment.NEGATIVE
    case 2    => Sentiment.NEUTRAL
    case 3, 4 => Sentiment.POSITIVE
}

Answer 1

这个怎么样:

def toSentiment(sentiment: Int): Sentiment = sentiment match {
    case 0 | 1 ? Sentiment.NEGATIVE
    case 2     ? Sentiment.NEUTRAL
    case 3 | 4 ? Sentiment.POSITIVE
}

请注意,此匹配并非详尽无遗.如果运行,可能会出现运行时错误,例如:toSentiment(5).一些短裤会警告你这件事.更安全的版本(假设其他任何数字都是中立的)可以是:

def toSentiment(sentiment: Int): Sentiment = sentiment match {
    case 0 | 1 ? Sentiment.NEGATIVE
    case 3 | 4 ? Sentiment.POSITIVE
    case _     ? Sentiment.NEUTRAL   
}