Hi, Libraries such as Hibernate often need to access private state of classes from other modules (e.g. when using field access for JPA entities).
Assuming that such library and the user's JAR are both provided as JPMS (named) modules, it had been my understanding so far [1], that the library should allow to pass in a MethodHandles.Lookup instance which has private access to the user's classes. This could be passed via a parameter during the library bootstrap, retrieved via a callback or similar. But discussing this with Alex Buckley at Devoxx Belgium last week, he suggested that this may not be the best level of abstraction. User code should never have to deal with low-level APIs such as Lookup, instead some sort of utility method should be provided by the library. It's not quite clear to me how this would look like, though. I can't see how a utility method in my library could obtain the Lookup, as MethodHandles#lookup() is caller-sensitive and must be invoked from within the module that wishes to grant private access to the library. So I'm curious whether there are any recommendations around this. Having some kind of documented API best practices for library authors in the same situation as me would be very helpful. I could also help to write that up, provided there's an agreed on pattern to do this. Thanks, --Gunnar [1] http://in.relation.to/2017/04/11/accessing-private-state-of-java-9-modules/#can-you-handle-the-var
