[lostcolony]

How do you move data? That Foo object that previously referenced both a Bar and a Baz, but you refactored it so now the Bar, not the Foo, has the reference to the Baz? Or where you changed the type of Baz from Gleep to Glorp?

Erlang, due to how actors encapsulate state, and dynamic typing, allows you to do those things pretty trivially.

[thu2111]

There are frameworks that support this kind of evolution, e.g. Kryo can do graph->graph transformations without intermediate serialisation I believe. Or you could write it by hand. If the static typing gets in the way you can always just use a scripting language to do it, many run on the JVM.