AFAIK this isn't possible yet in a straightforward way, and it boils down to limitations of the type system (lack of tuples resp. value types in general), and t

AFAIK this isn't possible yet in a straightforward way, and it boils down to limitations of the type system (lack of tuples resp. value types in general), and the (understandable) refusal of many to do it in way that's hacky and potentially slow. The discussion about this is actually quite old, for example: http://mail.openjdk.java.net/pipermail/lambda-libs-spec-observers/2013-June/002046.html http://mail.openjdk.java.net/pipermail/lambda-libs-spec-obse... IIRC that's a problem on bytecode level, that's why a (clean) solution still hasn't come up yet.