You're talking about Java I think, as generics and async are language features. I'm talking about the JVM. As far as I know, the performance and portability is

You're talking about Java I think, as generics and async are language features. I'm talking about the JVM. As far as I know, the performance and portability is unmatched. That said, reified generics I think are a limit of the JVM bytecode. But type erasure has its own advantages over reification. So one is not clearly better then the other, just offers a different set of trade offs.