如何在Scala Seq中移動項目？

Question

假設我有一個這樣的案例類：

case class Card(id: UUID, title: String)

和這樣的Bucket類：

case class Bucket(id: UUID, title: String, cards: Seq[Card]) {
 def moveCard(cardId: UUID, newIndex: Int): Bucket = 
   copy(cards = {
    ???
  })
}

如何填充moveCard（）方法以找到給定的卡並將其移動到序列中的新索引？

Answer 1

您可以使用兩倍劑量的patch()將項目移動到新位置。 不幸的是，根據前進或后退的方向有些不同。

case class Bucket(id: UUID, title: String, cards: Seq[Card]) {
  def moveCard(cardId: UUID, newIndex: Int): Bucket = {
    val from = cards.indexWhere(_.id == cardId)
    if (from < 0) throw new Error("no such card")
    copy(cards =
      if (from < newIndex)
        cards.patch(newIndex+1,Seq(cards(from)),0).patch(from,Seq(),1)
      else
        cards.patch(newIndex,Seq(cards(from)),0).patch(from+1,Seq(),1)
        )
  }
}

---

或@LeoC提供的非常好的簡化：

copy(cards = cards.patch(from, Seq(), 1).patch(newIndex, Seq(cards(from)), 0))