为什么我的Scala类型不匹配？

Question

我有以下变量series:

var series: List[FlotSerie] = List(
  new FlotSerie() {
    override val label = Full("Min")
  },
  new FlotSerie() {
    override val label = Full("Max")
  },
  new FlotSerie() {
    override val label = Full("Avg")
  }
)

不幸的是,我使用以下方法获得编译器错误,该方法采用新数据点并series使用List[FlotSeries]基于新数据和旧系列的新数据进行更新.

def updateSeries(sample: Sample): List[FlotSerie] = {
  series = series.map(serie =>
    serie match {
      case item if item.label == Full("Min") => {
        new FlotSerie() {
          override val label = item.label
          override val data = (sample.timestamp.toDouble, sample.min) :: serie.data
        }
      }
      case item if item.label == Full("Max") => {
        new FlotSerie() {
          override val label = item.label
          override val data = (sample.timestamp.toDouble, sample.max) :: serie.data
        }
      }
      case item if item.label == Full("Avg") => {
        new FlotSerie() {
          override val label = item.label
          override val data = (sample.timestamp.toDouble, sample.avg) :: serie.data
        }
      }
    }
  )
}

Scala编译器在重新分配时会因为发现类型不匹配而窒息:

error: type mismatch;
found   : Unit
required: List[net.liftweb.widgets.flot.FlotSerie]
   series = series.map(serie => serie match {

我在这做错了什么？它似乎应该返回一个可以分配给的List [FlotSeries] series.由于编译器发现Unit我想到了如何foreach总是返回Unit,我只是match操作符返回匹配表达式的最后一个值,而不是Unit.

Answer 1

Scala中的赋值返回Unit(又名Scala不完全为null),与返回指定值的Ruby不同.您的方法是尝试返回Unit而不是List [FlotSerie].

加:

return series

到您的方法,或将其更改为返回单位.

如果合适,您还可以使用案例类和正确匹配来简化代码:

  case class FlotSerie(label:Full, data:List[Tuple2[Double, Double]])
  var series: List[FlotSerie] = List( FlotSerie(Full("Min"), Nil), FlotSerie(Full("Max"), Nil), FlotSerie(Full("Avg"), Nil) )

  def updateSeries(sample: Sample): List[FlotSerie] = {
    series = series.map(serie => {
      serie.label match {
        case Full("Min") => FlotSerie(serie.label, (sample.timestamp.toDouble, sample.min) :: serie.data)
        case Full("Max") => FlotSerie(serie.label, (sample.timestamp.toDouble, sample.max) :: serie.data)
        case Full("Avg") => FlotSerie(serie.label, (sample.timestamp.toDouble, sample.avg) :: serie.data)
      }
    })
    return series
  }

我自己对Scala很新,所以YMMV.