scala根据参数扩展

Question

我想知道scala是否可以这样做： 假设我有以下课程：

trait Condition
trait BuyCondition extends Condition
trait SellCondition extends Condition

class OrCondition[C <: Condition](c1: C, c2: C) extends Condition

这可能使它像这样工作：

val buyOr: BuyCondition = new OrCondition[BuyCondition](bc1, bc2)
val sellOr: SellCondition = new OrCondition[SellCondition](sc1, sc2)

基本上我希望OrCondition可以是Sell或Buy，取决于它的类型参数。

Answer 1

是的，您可以使用phantom types

执行此操作

这是一个例子

// Define a base trait for the condition phantom type
object Condition {
  trait Type
}

// The Condition is paramaterised by the phantom type
trait Condition[T <: Condition.Type]

// Define Buy/Sell types
trait BuyType extends Condition.Type
trait SellType extends Condition.Type

// defin the buy/Sell conditions
type BuyCondition = Condition[BuyType]
type SellCondition = Condition[SellType]

class OrCondition[T <: Condition.Type](c1: Condition[T], c2: Condition[T]) extends Condition[T]

val bc1, bc2 = new BuyCondition {}
val sc1, sc2 = new SellCondition {}

val buyOr: BuyCondition = new OrCondition(bc1, bc2)
val sellOr: SellCondition = new OrCondition(sc1, sc2)

注意它们被称为幻像类型，因为类型BuyType和SellType在运行时从不实例化，它们仅存在于编译器中