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    <p>As of <a href="https://github.com/scala/scala/commit/f40e521b8f20bf8285b2f6871554a2bc637fe328">this commit</a> the magic incantation is slightly changed from what it was when Miles gave his excellent answer.</p> <p>The following works, but is it canonical? I hope one of the canons will correct it. (Or rather, cannons, one of the big guns.) If the view bound is an upper bound, you lose application to Array and String. It doesn't seem to matter if the bound is GenTraversableLike or TraversableLike; but IsTraversableLike gives you a GenTraversableLike.</p> <pre><code>import language.implicitConversions import scala.collection.{ GenTraversable=&gt;GT, GenTraversableLike=&gt;GTL, TraversableLike=&gt;TL } import scala.collection.generic.{ CanBuildFrom=&gt;CBF, IsTraversableLike=&gt;ITL } class GroupIdenticalImpl[A, R &lt;% GTL[_,R]](val r: GTL[A,R]) { def groupIdentical[That](implicit cbf: CBF[R, R, That]): That = { val builder = cbf(r.repr) def group(r: GTL[_,R]) { val first = r.head val (same, rest) = r.span(_ == first) builder += same if (!rest.isEmpty) group(rest) } if (!r.isEmpty) group(r) builder.result } } implicit def groupIdentical[A, R &lt;% GTL[_,R]](r: R)(implicit fr: ITL[R]): GroupIdenticalImpl[fr.A, R] = new GroupIdenticalImpl(fr conversion r) </code></pre> <p>There's more than one way to skin a cat with nine lives. This version says that once my source is converted to a GenTraversableLike, as long as I can build the result from GenTraversable, just do that. I'm not interested in my old Repr.</p> <pre><code>class GroupIdenticalImpl[A, R](val r: GTL[A,R]) { def groupIdentical[That](implicit cbf: CBF[GT[A], GT[A], That]): That = { val builder = cbf(r.toTraversable) def group(r: GT[A]) { val first = r.head val (same, rest) = r.span(_ == first) builder += same if (!rest.isEmpty) group(rest) } if (!r.isEmpty) group(r.toTraversable) builder.result } } implicit def groupIdentical[A, R](r: R)(implicit fr: ITL[R]): GroupIdenticalImpl[fr.A, R] = new GroupIdenticalImpl(fr conversion r) </code></pre> <p>This first attempt includes an ugly conversion of Repr to GenTraversableLike.</p> <pre><code>import language.implicitConversions import scala.collection.{ GenTraversableLike } import scala.collection.generic.{ CanBuildFrom, IsTraversableLike } type GT[A, B] = GenTraversableLike[A, B] type CBF[A, B, C] = CanBuildFrom[A, B, C] type ITL[A] = IsTraversableLike[A] class FilterMapImpl[A, Repr](val r: GenTraversableLike[A, Repr]) { def filterMap[B, That](f: A =&gt; Option[B])(implicit cbf : CanBuildFrom[Repr, B, That]): That = r.flatMap(f(_).toSeq) } implicit def filterMap[A, Repr](r: Repr)(implicit fr: ITL[Repr]): FilterMapImpl[fr.A, Repr] = new FilterMapImpl(fr conversion r) class GroupIdenticalImpl[A, R](val r: GT[A,R])(implicit fr: ITL[R]) { def groupIdentical[That](implicit cbf: CBF[R, R, That]): That = { val builder = cbf(r.repr) def group(r0: R) { val r = fr conversion r0 val first = r.head val (same, other) = r.span(_ == first) builder += same val rest = fr conversion other if (!rest.isEmpty) group(rest.repr) } if (!r.isEmpty) group(r.repr) builder.result } } implicit def groupIdentical[A, R](r: R)(implicit fr: ITL[R]): GroupIdenticalImpl[fr.A, R] = new GroupIdenticalImpl(fr conversion r) </code></pre>
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