Scala模式与Mixins匹配

戴维·H

我想增强基于混合技术的模式匹配，例如：

trait Base {
  def match(x:Any):String
}

trait HandleAString {
  def match(x:Any):String = x match {
     case "A" => "matched A string"
  }
}

trait HandleOneInt {
  def match(x:Any):String = x match {
     case x:Int if (x==1) => "matched 1 int"
  } 
}


//main 
val handler = new Base extends HandleOneInt with HandleAString 
println(handler.match("a") ) //should print  "matched A string"
println(handler.match(1) )  //should print  "matched 1 int"
println(handler.match(2) )  //should throw exception

如果您有任何其他技术，我想听听...

毫米

老实说，混入方面有点过度抽象-我敦促您仔细考虑您实际想要实现的目标，并寻找一种更简单的方法。我在mixin方面无济于事，但是您可以将单个匹配用例存储为a，PartialFunction然后将多个using组合使用orElse，这可能会满足您的要求，或者至少会为您指明前进的方向：

val handler1: PartialFunction[Any, String] = {
  case "A" => "matched A string"
}
val handler2: PartialFunction[Any, String] = {
  case x:Int if (x==1) => "matched 1 int"
}

val manyHandlers = List(handler1, handler2)
val handler = manyHandlers.reduce(_.orElse(_))

println(handler("A") ) // "a" won't match, match is exact
println(handler(1) )
println(handler(2) )

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