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POScala TypeTags or Manifest: Is it possible to determine if a type is a Value class?
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  1. POScala TypeTags or Manifest: Is it possible to determine if a type is a Value class?
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    copied!<p>How do I find out if an object is a value class type, so that in the following example the test would print that the id is an AnyVal?</p> <pre><code>class MyId(val underlying: Int) extends AnyVal class AnyValSuite extends FunSuite { class Sample { def doIt[T](t: T)(implicit tag: TypeTag[T]): Unit = { if(???) println(s"$t is an AnyVal") } } test("Getting info if a type is a value class") { new Sample().doIt(new MyId(1)) } } </code></pre> <p>@senia: Thanks for the answer. Works perfect. Is it also possible to find out the primitive type the Value class is wrapping?</p> <p>Extended the example now:</p> <pre><code>class MyId(val underlying: Int) extends AnyVal class NonAnyValId(val underlying: Int) class AnyValSuite extends FunSuite { class Sample { def doIt[T](t: T)(implicit tag: TypeTag[T]): Unit = { if(implicitly[TypeTag[T]].tpe &lt;:&lt; typeOf[AnyVal]) println(s"$t is an AnyVal") else println(s"$t is not an AnyVal") } } test("Getting info if a type is a value class") { new Sample().doIt(new MyId(1)) new Sample().doIt(new NonAnyValId(1)) new Sample().doIt(1) } } </code></pre> <p>returns:</p> <pre><code>MyId@1 is an AnyVal NonAnyValId@38de28d is not an AnyVal 1 is an AnyVal </code></pre> <p><strong>Edit 2:</strong> Now with wrapped type checking:</p> <pre><code>import org.scalatest.FunSuite import scala.reflect.runtime.universe._ class MyId(val underlying: Int) extends AnyVal class NonAnyValId(val underlying: Int) class AnyValSuite extends FunSuite { class Sample { def doIt[T](t: T)(implicit tag: TypeTag[T]): Unit = { val tpe= implicitly[TypeTag[T]].tpe if(tpe &lt;:&lt; typeOf[AnyVal]) { println(s"$t is an AnyVal") val fields = tpe.members.filter(! _.isMethod) fields.size match { case 0 =&gt; println("has no fields, so it's a primitive like Int") case 1 =&gt; { println("has a sole field, so it's a value class") val soleValueClassField = fields.head.typeSignature println("of type: " + soleValueClassField) if(typeOf[Int] == soleValueClassField) println("It wraps a primitive Int") } case 2 =&gt; throw new Exception("should never get here") } } else println(s"$t is not an AnyVal") } } test("Getting info if a type is a value class") { new Sample().doIt(new MyId(1)) println new Sample().doIt(new NonAnyValId(1)) println new Sample().doIt(1) } } </code></pre> <p>returns:</p> <pre><code>MyId@1 is an AnyVal has a sole field, so it's a value class of type: Int It wraps a primitive Int NonAnyValId@3d0d4f51 is not an AnyVal 1 is an AnyVal has no fields, so it's a primitive like Int </code></pre> <p>Just wondering if there is some easier solution?</p>
 

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