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Comment by pulse7 | Hacker News Reader

It takes time to make such a fundamental, but backwards compatible change for 10 million developers... Nobody wants Python 2 -> 3...

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It's a new keyword & bytecode feature, so there's no backwards compatible risks to it. Nobody's existing code would be impacted as nobody's existing code is using user-defined value types in the byte code.

It looks like there were some experiments and prototyping out of Valhalla from 2014-2018 (including a publicly available build: https://jaxenter.com/java-value-type-163446.html ), but there doesn't seem to be any updates since then

It's being actively worked on [1, 2].

[1] https://github.com/openjdk/valhalla/ [2] https://mail.openjdk.java.net/pipermail/valhalla-dev/

> there doesn't seem to be any updates since then

Oracle (Brian Goetz in particular) regularly gives talks and interviews and publishes updates.

There was even a link on this site a couple weeks ago: https://news.ycombinator.com/item?id=28364500

They don't want to introduce the a third type (next to primitive types and reference types). They are unifying the type system so that after this change we will also get universal generics so that List<T> could be List<int>, List<Person> and also List<Person.val> (where Person.val is an inlined class without identity).

But introducing such a large scale change to the JVM has to be well thought out, especially when it will get to live for decades.

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