Pattern matching via switch?

[DanielG]

I've been playing around with this via inheritance lately (I'm 
aware of the sumtype package but specifically wanted to use 
objects instead of structs), had some good results.

It involves a bit of boilerplate though. I'm essentially using 
the visitor pattern + an anonymous class implementing a matcher 
interface:

https://gist.github.com/dewf/dadc0f2775b40b65a3ebf7458d3c2c79

I would love to use templated return values from the match() 
method, though. Does anybody know how to do that without the 
compiler complaining ("'final' functions cannot be 'abstract'") ?

Specifically, is there any way to make:

    abstract void match(Matcher m);

Become:

    abstract T match(T)(Matcher!T m);

?