Immutable record types as the default, most-used way of modeling data is a great idea that some languages cater to and other languages force you to do in weird,

Immutable record types as the default, most-used way of modeling data is a great idea that some languages cater to and other languages force you to do in weird, hacky ways. Countless systems have been designed around mutable data simply because they were written in languages where mutable data was the default. I personally worked on several Java systems where mutability was used but was trivial to refactor out, because every place an instance was modified, it was simple to construct a new instance instead. On a couple of them I had ownership of the codebase and was able to complete this refactoring with a reasonable amount of effort. I also created a small codebase in Java with an immutable data model, only to pass it off to someone who immediately added setters for every field because they were "missing." And then of course he started to find uses for them. I don't have a desire to work in Java again, but I think Java recognizing immutable record classes as a concept worthwhile of first class language support is a significant step forward for the industry.