for循环在匹配表达式后不返回列表中的值

Question

我在 for 循环中使用了使用 yield 的匹配表达式，但我没有得到想要的结果

   val daysOfWeek = List("Mon","Tues","Wed","Thur","Fri","Sat","Sun")
        val day = "Mon"
         for (day <- daysOfWeek) yield
        {
          day match 
          {
            case "Mon" => "is boring"
            case otherDay => otherDay
              print(day)
          }
}

O/p 上面的代码是 (TuesWedThurFriSatSun) 但我想要 o/p 像 (is boringTuesWedThurFriSatSun)

我怎样才能做到这一点？

Answer 1

问题是您在 otherday case 块中打印，因此您将其作为输出。

这是您想要实现的目标：

 val daysOfWeek = List("Mon","Tues","Wed","Thur","Fri","Sat","Sun")
 val day = "Mon"
 for (day <- daysOfWeek) yield
 {
     val output = day match
     {
        case "Mon" => "is boring"
        case otherDay => otherDay
     }
     print(output)
 }

输出：

is boringTuesWedThurFriSatSun

Answer 2

考虑将模式匹配分解到它自己的函数中

val boringDay: String => String = {
  case "Mon" => "is boring"
  case otherDay => otherDay
}

可用于转换列表

daysOfWeek.map(boringDay) // List(is boring, Tues, Wed, Thur, Fri, Sat, Sun)

现在使用 mkString 获取可打印字符串

val output = daysOfWeek.map(boringDay).mkString("")
println(output)

输出

res1: String = is boringTuesWedThurFriSatSun

for循环在匹配表达式后不返回列表中的值

for loop not returning value in list after matching the expression

for-loop

scala

yield

match