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POAvoiding explicit casts in Factory
 

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  1. POAvoiding explicit casts in Factory
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    <p>I have an external DSL (Combinator-Parsers) to define <code>Extractor[A]</code> where A is the type that is extracted when the Extractor has been executed.</p> <p>An extractor consists of steps that call the next step as the continuation. The extractor creates intermediate extractions (string-based key/value-pairs), which are finally transformed into the proper <code>A</code>s by a factory.</p> <p>Extractor: <code>case class Extractor[A](id: String, start: Step[A], factory: Factory[A])</code></p> <p>Step: <code>sealed trait Step[A] { def process(ctx: Context[A]): List[A] }</code></p> <p>Factory: <code>trait Factory[A] { def create(extracts: List[(String,String)]): List[A] }</code></p> <p>Currently my extractor-parser looks like the following:</p> <pre><code> val extractor: Parser[Extractor[_]] = trace ~ "EXTRACT" ~ extractorType ~ extractorId ~ step ^^ { case t ~ _ ~ ty ~ id ~ step =&gt; { val extr = ty match { case "SUBTITLES" =&gt; { Extractor[MovieInfos.Subtitle](id, step.asInstanceOf[Step[MovieInfos.Subtitle]], new SubtitleFactory) } case x =&gt; throw new InvalidExtractorType(x) } extr.trace(t) } } </code></pre> <p><strong>EDIT</strong>: The step-parser has signature <code>val step: Parser[Step[_]]</code> (the step-parser is not able to know that type of <code>Step[A]</code> it is exactly parsing. Finally the step gets its proper <code>A</code>-type by the extractor-parser's <code>asInstanceOf</code>)</p> <p>The above extractor parser is currently only able to parse extractors of extractorType <code>"SUBTITLES"</code>. I want to add other extractorTypes successively, e.g. <code>case "REVIEWS" =&gt; ...</code>.</p> <p>For each extractor <code>Extractor[A]</code>, I have to provide a specialized factory (e.g. <code>new SubtitleFactory</code>) that creates things of type <code>A</code> (e.g. <code>MovieInfos.Subtitle</code>) and pass matching <code>step</code>s into the extractor (that's what the <code>asInstanceOf</code> is for).</p> <p>The parser has to parse different Extractor-Types (Subtitles, Images, Audiotracks, etc.), so I use <code>Parser[Extractor[_]]</code>, is this properly typed or is there any better way?</p> <p>Furthermore, I want to avoid that <code>step.asInstanceOf[Step[MovieInfos.Subtitle]]</code> which looks a bit fishy since I already provided the proper type <code>Extractor[MovieInfos.Subtitle]</code></p> <p>And finally I want a more flexible Factory, possibly extensible by some sort of configuration/hooks. </p> <p>Any recommendations appreciated, thanks.</p>
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    1. UShotzen
    1. UShotzen
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      1. VTUpMod
    1. COMaybe try `def extractor[T]: Parser[Extractor[T]] = ...`
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      1. USLuigi Plinge
    2. COI do not know the type of the resulting extractor when calling the parser.
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      1. UShotzen
    3. CO... ~ (step: Step[MovieInfos.Subtitle]) => ...
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      1. USAlex
 

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