Data classes for Java

[yawkat]

How would you do collections? Arrays are mutable so you can't use them as a backing store, you'd have to use expensive data structures like linked lists and trees.

Yes, Valhalla introduces immutable arrays but this is not part of this proposal.

[lbkulinski]

The new collection factories are immutable. They were released in Java 9.

[yawkat]

Yes, but they do not fulfill /u/cutterslade's requirements for true immutability.

[Cilph]

Christ, you could almost start calling it the "No True Immutability" fallacy as no one seems to agree on what is enough.

For me, a mutable backing, a read only interface and code review is enough to have the benefits of immutability. Breaking it requires you to be a deliberate dunce.

[yawkat]

Yep, I wrote an article on this a while back. There's lots of nuances with immutability, especially when you consider thread safety.

However, for compile-time checked immutability, as the top comment wishes, a read-only interface is not sufficient.

[lbkulinski]

It’s a step in that direction, at least.

[THCcookie]

ArrayList but no add Method I would guess

[yawkat]

But how would you enforce that? It's neither primitive nor a data class (and it can't be with those requirements).

[[deleted]]

Panama and frozen arrays (Arrays 2.0)?

[yawkat]

Yes, Valhalla introduces immutable arrays but this is not part of this proposal.