Variants/case classes/algebraic data types/sums/oh my! (original) (raw)

Brian Goetz brian.goetz at oracle.com
Sat Jun 11 16:24:06 UTC 2016

To amplify John's comments -- we are very interested in these topics, but we believe there are some fundamentals that have to be addressed first. No need to dive into great detail about how great case classes / destructuring pattern matches are; we are more than aware :)

I believe that all of the existing languages could benefit from both JVM and Java language support for the types, and I believe that support could be provided with minimal, non-intrusive changes to the virtual machine (an extra piece of class metadata, no new bytecode instructions, a couple of extra syntax rules in the Java language that likely build upon the existing switch statement, and no new keywords).

By way of setting expectations .... there are no minimal, non-intrusive language or JVM features. Usually, it requires a tremendous amount of work to make a feature merely seem less intrusive; consider lambdas, which are "just" function literals -- except making them work required entirely overhauling type inference and method overload selection -- which if done right, no one notices.

That said, we're willing to invest in big features -- but as John mentioned, there are some things ahead of this one on the queue, which are probably prerequisites for doing this well. (For example, value types are a prerequisite for useful tuples.)

So, with those expectation-settings comments aside, we're interested to see what you come up with, and we encourage you to follow the valhalla discussions to see where we're going. (In particular, I'm interested in hearing what you think the VM is missing for these features.)

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