Re: Proposal: create an Extractor for PartialFunction
杨博 <[email protected]>
| Newsgroups | gmane.comp.lang.scala |
|---|---|
| Message-ID | <[email protected]> |
BTW: At the moment, all the other answers on the discussion <at http://stackoverflow.com/questions/5902266/inverse-of-partialfunctions-lift-method> except mine are wrong because they did not implement getOrElse. 在 2015年7月9日星期四 UTC+8下午10:43:15，Vlad Patryshev写道： > > Here's some discussion of this issue: > http://stackoverflow.com/questions/5902266/inverse-of-partialfunctions-lift-method > > Instead of going back into the world of booleans and conditions, I'd > suggest to think about why there's no such thing already available. Maybe > this is the right direction. applyOrElse is total; if it does not work > for you, lift should. It is pretty scientific, and gets you to a Kleisli > category. All these ifs and match/cases are a little bit like crutches. > > Thanks, > -Vlad > > On Wed, Jul 8, 2015 at 9:56 PM, 杨博 <[email protected] <javascript:>> > wrote: > >> Sometimes, when I create a method, I need an extractor parameter for >> pattern matching, while there is not a generic extractor trait in the Scala >> Standard Library. So we have to use a PartialFunction as the parameter >> instead. >> >> >> When I use the PartialFunction, I had to create pattern matching >> expression like this. >> >> >> input match { >> >> case x if partialFunction.isDefined(x) => >> >> val data = partialFunction.apply(x) >> >> doSomethingWith(data) >> >> } >> >> >> This approach is not perfect because: >> >> >> 1. partialFunction.isDefined and partialFunction.apply checked x >> twice, which is slow if isDefined has complex logical, checking >> whether a file exists for example. >> 2. The if condition around temporary variable x is too trivial. >> >> I think the better approach is converting the PartialFunction to an >> extractor and matching with that extractor >> >> >> implicit final class PartialFunctionAsExtractor[A, B](pf: >> PartialFunction[A, B]) { >> >> object Extractor { >> >> def unapply(a: A) = PartialFunction.condOpt(a)(pf) >> >> } >> >> } >> >> >> input match { >> case partialFunction.Extractor(data) => >> doSomethingWith(data) >> } >> >> Since this is a common approach, I hope adding the >> PartialFunctionAsExtractor to scala.Predef . >> >> I would like to create a pull request if people like this idea. >> >> -- >> You received this message because you are subscribed to the Google Groups >> "scala-language" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected] <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > > -- You received this message because you are subscribed to the Google Groups "scala-language" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.