Re: Proposal: create an Extractor for PartialFunction

Don't either PartialFunction.lift or PartialFunction.applyOrElse do pretty
much exactly what you want?

On Thu, 9 Jul 2015 at 05:56 杨博 <[email protected]> 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.
>
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