We should do an assessment of our AST transformations cf the immutables.org library

https://immutables.github.io/

It would be good to see if there are any feature gaps or nicer ways of doing things compared with what we offer in Groovy. Sometimes we offer the features in a different way, so it isn't just a case of trying to copy everything they offer. This issue is just about doing an assessment of what good ideas we might consider taking on board. We can create further issues to actually do the work.