如何将此 SetLike 集合从 Scala 2.12 转换为 2.13？

Posted 2023-03-23

【中文标题】如何将此 SetLike 集合从 Scala 2.12 转换为 2.13？

【英文标题】：How to convert this SetLike collection from Scala 2.12 to 2.13?

【发布时间】：2021-06-21 11:33:41

【问题描述】：

我有这个简单的不可变的基于 Long 的位集，其中包含 Card 案例类。不幸的是，随着 Scala 2.13 集合的改进，它不再编译了。

我看过 Scala 2.13 中的 BitSet 实现，但它非常冗长。我将如何在保持代码简洁明了的同时转换这个类？有没有我可以构建的这种数据结构的演示示例？

import scala.collection.GenSet, GenTraversableOnce, SetLike

case class Card(ord: Int)

case class Deck(data: Long) extends Set[Card] with SetLike[Card, Deck] 
    def iterator = new Iterator[Card] 
        var cur = data

        def next = 
            val res = java.lang.Long.numberOfTrailingZeros(cur)
            cur &= ~(1L << res)
            Card(res)
        

        def hasNext = cur != 0
    

    override def empty: Deck = Deck.empty
    override def size: Int = java.lang.Long.bitCount(data)
    override def contains(card: Card): Boolean = (data & (1L << card.ord)) > 0
    override def +(card: Card): Deck = Deck(data | (1L << card.ord))
    override def -(card: Card): Deck = Deck(data & ~(1L << card.ord))

    private def toBits(deck: GenTraversableOnce[Card]): Long = deck match 
        case deck: Deck => deck.data
        case _ =>
            var data = 0L
            for (card <- deck) data |= 1L << card.ord
            data
    

    override def ++(deck: GenTraversableOnce[Card]): Deck = Deck(data | toBits(deck))
    override def &(deck: GenSet[Card]): Deck = Deck(data & toBits(deck))
    override def diff(deck: GenSet[Card]): Deck = Deck(data & ~toBits(deck))


object Deck 
    val empty: Deck = Deck(0)
    def of(deck: Iterable[Card]): Deck = empty ++ deck

【参考方案1】：

应该是这样的；我已经评论了值得注意的步骤

// SetLike has been sorta superseded by SetOps. Notice the 3rd type parameter -
// that's the return constructor of e.g. deck.map(Some(_))
case class Deck(data: Long) extends Set[Card] with SetOps[Card, Set, Deck] 
  
  // Minimum definition of set is these two, instead of symbolic names
  override def incl(card: Card): Deck = Deck(data | (1L << card.ord))
  override def excl(card: Card): Deck = Deck(data & ~(1L << card.ord))

  def iterator = new Iterator[Card] 
    var cur = data

    def next() = 
      val res = java.lang.Long.numberOfTrailingZeros(cur)
      cur &= ~(1L << res)
      Card(res)
    

    def hasNext = cur != 0
  

  override def empty: Deck = Deck.empty
  override def size: Int = java.lang.Long.bitCount(data)
  override def contains(card: Card): Boolean = (data & (1L << card.ord)) > 0

  // These two are inherited from SetOps but neither their type nor the impl aligns with
  // what you want them to do. You have to re-override them to type as Deck instead of Set[Card]
  override protected def fromSpecific(coll: IterableOnce[Card]): Deck = Deck(toBits(coll))
  
  override protected def newSpecificBuilder: Builder[Card, Deck] =
    new Builder[Card, Deck] 
      var data = 0L
      def clear(): Unit = data = 0
      def result(): Deck = Deck(data)
      def addOne(elem: Card): this.type = 
        data |= (1L << elem.ord)
        this
      
    

  // I kept this as is but you can probably replace it with newSpecificBuilder
  // if you want to keep things more DRY - you could use
  // `newSpecificBuilder.addAll(deck).result()` in fromSpecific
  private def toBits(deck: IterableOnce[Card]): Long = deck match 
    case deck: Deck => deck.data
    case _ =>
      var data = 0L
      for (card <- deck.iterator) data |= 1L << card.ord
      data
  

  
  // concat is the only non-final method - union and | just delegate to that.
  override def concat(deck: IterableOnce[Card]): Deck = Deck(data | toBits(deck))
  
  // this needs a set of unknown-mutability. It has kinda replaced GenSet
  override def diff(deck: scala.collection.Set[Card]): Deck = Deck(data & ~toBits(deck))