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copied!<p>(Not a complete solution, but might give some ideas)</p> <p>One impressive feature of Scala is its ability to return a list of Fruits when an orange is appended to a list of apples. It's fine with values, precisely because you let the generic type be inferred.</p> <pre><code>import scala.reflect.Manifest def CommonSuperType[A, B >: A : Manifest](a:A, b:B) = manifest[B] </code></pre> <p>It works (kind of) :</p> <pre><code>scala> CommonSuperType(new JButton, new JPanel) res42: Manifest[javax.swing.JComponent with javax.accessibility.Accessible] = javax.swing.JComponent with javax.accessibility.Accessible </code></pre> <p>Next step would be to lift this trick to higher kinded types (not tested).<br> An half baked solution consists in creating values from types (cf <a href="https://stackoverflow.com/questions/818996/abstract-types-type-parameters-in-scala">this answer</a>) :</p> <pre><code>class CommonSuper[A:Manifest, B:Manifest] { def make[T:Manifest] = manifest[T].erasure.newInstance.asInstanceOf[T] val instanceA = make[A] val instanceB = make[B] def getType = CommonSuperType(instanceA, instanceB) } </code></pre> <p>But I'm stuck in this unintuitive inconsistency :</p> <pre><code>scala> val test = new CommonSuper[JButton, JPanel] scala> test.getType res66: Manifest[Any] = Any scala> CommonSuperType(test.instanceA, test.instanceB) res67: Manifest[javax.swing.JComponent with javax.accessibility.Accessible] = javax.swing.JComponent with javax.accessibility.Accessible </code></pre> <p>Anyway, whereas I'm fond of this type of questions (questions about types), here it smells like an <a href="https://meta.stackexchange.com/questions/66377/what-is-the-xy-problem">XY Problem</a>.</p>

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