[英]Scala pattern matching - match multiple successful cases
I am fairly new to Scala, and would like to know if it is possible for a match
to execute multiple matching cases at once. 我对Scala相当新,并且想知道match
是否可以同时执行多个匹配的情况。 Without getting into too much detail, I am basically working on a function that "scores" a certain piece of text according to various traits; 在没有深入细节的情况下,我基本上致力于根据各种特征“评分”某段文字的功能; these traits can overlap, and multiple traits can be true for one given string. 这些特征可以重叠,并且对于一个给定的字符串,多个特征可以为真。
To illustrate what I want in code, it would look something like this: 为了说明我想要的代码,它看起来像这样:
Say we have a String, str
, with a value of "Hello World". 假设我们有一个String, str
,其值为“Hello World”。 I would like something along the lines of the following: 我想要的是以下几点:
str match {
case i if !i.isEmpty => 2
case i if i.startsWith("world") => 5
case i if i.contains("world") => 3
case _ => 0
}
I would like the above code to trigger both the first and third conditions, effectively returning both 2 and 3 (as a tuple or in any other way). 我想上面的代码,以触发所述第一和第三个条件,有效地返回既2和3(作为一个元组或以任何其他方式)。
Is this possible? 这可能吗?
Edit: I know this can be done with a chain of if
's, which is the approach I took. 编辑:我知道这可以通过一系列if
来完成,这就是我采用的方法。 I'm just curious if something like the above implementation is possible. 我很好奇是否可以实现上述实现。
You can turn your case
statements to functions 您可以将case
语句转换为函数
val isEmpty = (str: String) => if ( !str.isEmpty) 2 else 0
val startsWith = (str: String) => if ( str.startsWith("world")) 5 else 0
val isContains = (str: String) => if (str.toLowerCase.contains("world")) 3 else 0
val str = "Hello World"
val ret = List(isEmpty, startsWith, isContains).foldLeft(List.empty[Int])( ( a, b ) => a :+ b(str) )
ret.foreach(println)
//2
//0
//3
You can filter the 0 values with filter
您可以过滤与0值filter
val ret0 = ret.filter( _ > 0)
ret0.foreach(println)
Please, consider this solution: 请考虑这个解决方案:
val matches = Map[Int, String => Boolean](2 -> {_.isEmpty}, 3 -> {_.contains("world")}, 5 -> {_.startsWith("world")})
val scores = matches.filter {case (k, v) => v(str)}.keys
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