Scala模式与mixin匹配

Question

我想基于mixin技术增强模式匹配,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  

如果你有任何其他技术我想听到...

Answer 1

老实说,混合方面有过度抽象的气味 - 我敦促你仔细思考你实际想要实现的目标,并寻找一种更简单的方法.我无法帮助mixin方面,但你可以将一个匹配案例存储为一个PartialFunction并使用几个组合orElse,这可能会做你想要的或者至少指向你想要的方向:

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) )