Re: Proposal: create an Extractor for PartialFunction

No, neither lift nor applyOrElse is an extractor.

In fact, the extractor I proposed calls condOpt, which calls applyOrElse
internally.

Alec Zorab <[email protected]>于2015年7月9日周四 下午4:12写道：

> 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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杨博 (Yang Bo)

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