Github user MattWhelan commented on the pull request:
https://github.com/apache/spark/pull/4165#issuecomment-71105198
@vanzin
The way the registration method works is also really weird. It takes no
params, you'll notice. In ClassLoader, it calls a Reflection native method to
actually get a reference to the *caller's* Class. Which feels all kinds of
horrible to me, though it does make for a really simple interface (in Java).
But, the upshot is that registerAsParallelCapable() must be called from the
class being registered, before an instance of that class has been created. So
basically, a static initializer.
Since there aren't real static methods in Scala, I don't think the factory
thing would work. Even though you could probably get the timing right, the next
level down the stack would be a companion object class, or something, not the
CL itself.
Really, I'm pretty OK with that. ClassLoaders and all their related issues
are deep JVM voodoo. It's a low-level concept, and Scala is a high level
language.
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