Scala - 使自定义类型协变

Question

我想用 type 关键字创建两个自定义类型，并使它们与其他类型协变，以便我可以将它们放在一个列表或映射中并通过模式匹配使用它，这可能吗？

type Reaction

type Condition = () => Boolean

type ComplexReaction extends Reaction = (Condition) => Unit
type SimpleReaction extends Reaction = () => Unit

val map = Map[Condition, Reaction]

def addPair(c: Condition, a: Reaction) { map += (c -> a) }

def executeAll {
  for(puffy <- map) puffy match {
    case (c, a: ComplexReaction) => a(c)
    case (c, a: SimpleReaction) => if(c) a()
  }
}

当然，这种type 构造在Scala 中是不允许的。有什么方法可以达到类似的结果，还是我必须制作两个单独的地图？

Answer 1

这可能是一种好方法。

type Condition = () => Boolean

sealed trait Reaction
case class ComplexReaction(a: (Condition) => Unit) extends Reaction
case class SimpleReaction(a: () => Unit) extends Reaction

val map = Map[Condition, Reaction]

def addPair(c: Condition, a: Reaction) { map += (c -> a) }

def executeAll {
  for(puffy <- map) puffy match {
    case (c, ComplexReaction(a)) => a(c())
    case (c, SimpleReaction(a)) => if(c()) a()
  }
}

附带说明一下，这是我在 Haskell 中通常会做的事情（将任何冲突的 types 更改为 newtypes）。

Answer 2

我有几乎相同的解决方案，我简化了 Condition 类型，添加了按名称参数调用并将映射更改为可变：

type Condition = Boolean

sealed abstract class Reaction

case class ComplexReaction(rec: (=> Condition) => Unit) extends Reaction

case class SimpleReaction(rec: () => Unit)  extends Reaction 


var map = Map[Condition, Reaction]()

def addPair(c: Condition, a: Reaction) { map += (c -> a) }

def executeAll {
for(puffy <- map) puffy match {
case (c, ComplexReaction(i)) => i(c)
case (c, SimpleReaction(i)) => if(c) i()
}
}