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POReflection with Typeclasses
 

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    <p>I'm writing a little registration module for some application and doing this with typeclasses. Main logic is based on Spray routing:</p> <pre><code>val api = post { path("register" / Rest) { rest =&gt; rest match { case "user" =&gt; register[User] // ... other cases } } } } </code></pre> <p>To simplify i have the following data type for User:</p> <pre><code>case class User(id: String, email: String) </code></pre> <p>And to extract entity from POST request i'm using typeclass:</p> <pre><code>trait EntityExtractor[T] { def extractFromRequest: Directive[T :: String :: HNil] } </code></pre> <p>implementation for user:</p> <pre><code>object User { implicit val extractor = new EntityExtractor[User] { def extractFromRequest: Directive[User :: String :: HNil] = formFields('email, 'pass).hmap { case email :: pass :: HNil =&gt; val id = UID.genId User(id, email) :: pass :: HNil } } } </code></pre> <p>The problem arises in my register method which uses a typeclass directive:</p> <pre><code>def register[T] = extractEntity[T].apply { entity =&gt; // fails here validateEntity(entity) { completeRegistration(entity) } } } def extractEntity[T: EntityExtractor]: Directive[Entity[T] :: HNil] = { implicitly[EntityExtractor[T]].extractFromRequest.hmap { case entity :: pass :: HNil =&gt; Entity(entity, pass) :: HNil } } </code></pre> <p>And it fail with an exception: <code>could not find implicit value for evidence parameter of type EntityExtractor[T]</code>.</p> <p>Is there any way to fix this with reflection (TypeTags or Manifest) <strong>without pattern matching</strong>?</p>
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