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    copied!<p>Not really the precise answer, but two observations - Scala 2.10 will give you a nicer error:</p> <pre><code>scala&gt; s.flatMap(_.getEnumConstants) &lt;console&gt;:9: error: no type parameters for method flatMap: (f: Class[_ &lt;: Enum[_]] =&gt; scala.collection.GenTraversableOnce[B])(implicit bf: scala.collection.generic.CanBuildFrom[Seq[Class[_ &lt;: Enum[_]]],B,That])That exist so that it can be applied to arguments (Class[_ &lt;: Enum[_]] =&gt; scala.collection.mutable.ArrayOps[(some other)_$1(in object $iw) with Object] forSome { type (some other)_$1(in object $iw) &lt;: Enum[_] }) --- because --- argument expression's type is not compatible with formal parameter type; found : Class[_ &lt;: Enum[_]] =&gt; scala.collection.mutable.ArrayOps[(some other)_$1(in object $iw) with Object] forSome { type (some other)_$1(in object $iw) &lt;: Enum[_] } required: Class[_ &lt;: Enum[_]] =&gt; scala.collection.GenTraversableOnce[?B] s.flatMap(_.getEnumConstants) ^ &lt;console&gt;:9: error: type mismatch; found : Class[_ &lt;: Enum[_]] =&gt; scala.collection.mutable.ArrayOps[(some other)_$1(in object $iw) with Object] forSome { type (some other)_$1(in object $iw) &lt;: Enum[_] } required: Class[_ &lt;: Enum[_]] =&gt; scala.collection.GenTraversableOnce[B] s.flatMap(_.getEnumConstants) ^ &lt;console&gt;:9: error: Cannot construct a collection of type That with elements of type B based on a collection of type Seq[Class[_ &lt;: Enum[_]]]. s.flatMap(_.getEnumConstants) ^ </code></pre> <p>And, if you split your <code>flatMap</code>, you get to see a simpler version of the issue:</p> <pre><code>scala&gt; s.map(_.getEnumConstants) res28: Seq[Array[_$1 with Object] forSome { type _$1 &lt;: Enum[_] }] = List(Array(NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS, MINUTES, HOURS, DAYS), Array(RELEASE_0, RELEASE_1, RELEASE_2, RELEASE_3, RELEASE_4, RELEASE_5, RELEASE_6)) scala&gt; res28.flatten &lt;console&gt;:10: error: No implicit view available from Array[_$1 with Object] forSome { type _$1 &lt;: Enum[_] } =&gt; scala.collection.GenTraversableOnce[B]. res28.flatten ^ </code></pre> <p>That is rather surprising since you'd think that it should be easy to turn an <code>Array</code> into a <code>GenTraversableOnce</code>. I don't have time to dig out the details at the moment, but I'll point out that the following things seem to work:</p> <pre><code>s.flatMap(_.getEnumConstants.toSeq) s.flatMap(_.getEnumConstants.map(_.asInstanceOf[Enum[_]])) </code></pre> <p>I vote compiler bug, because of <a href="https://gist.github.com/themel/5141394" rel="nofollow">this gist</a>, which shows some very weird behaviour in the REPL for this simple script</p> <pre><code>val s: Seq[Class[_ &lt;: java.lang.Enum[_]]] = Seq(classOf[java.util.concurrent.TimeUnit], classOf[javax.lang.model.SourceVersion]) s.flatMap(_.getEnumConstants.toSeq) s.flatMap(_.getEnumConstants.toArray) 1234 </code></pre>
 

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