> From: "Caleb" <[email protected]> > To: "dev" <[email protected]> > Sent: Monday, April 13, 2026 3:11:55 PM > Subject: Re: [JVM Question] Making Friends with Ad-Hoc Classes
> I know how to emit ad-hoc classes - I also know that hidden classes > specifically > don't have an entry in the symbol table you mean their name is not registered inside a classloader, > and can be GC'd, that depends on the ClassOptions you provide (see ClassOption.STRONG) > making them particularly useful for single-function classes - I just don't > know > how you'd make a class you don't know the name of a friend/innerclass. defineHiddenClass takes a lookup as parameter and if you use ClassOption.NESTMATE then the defined class is a nestmate of the lookupClass of the Lookup. Caleb, if you want to know more, email me directly, because it starts to be OT for the goovy-dev mailing list. regards, Rémi > On Mon, Apr 13, 2026, 3:13 AM Remi Forax < [ mailto:[email protected] | > [email protected] ] > wrote: >>> From: "Caleb" < [ mailto:[email protected] | [email protected] ] > >>> To: "dev" < [ mailto:[email protected] | [email protected] ] > >>> Sent: Sunday, April 12, 2026 10:09:35 PM >>> Subject: [JVM Question] Making Friends with Ad-Hoc Classes >>> Hi! This isn't really related to Groovy, but I'm doing weird things with >>> the JVM >>> for a compiler plugin and I've hit a knowledge barrier I can't pass. Since >>> you >>> guys are the experts on "doing weird stuff with the JVM", I was hoping you >>> might be willing to help? >>> My goal is to copy existing methods, transform them, and link to those >>> transformed versions with InvokeDynamic. Basically the template system from >>> C++, but done at runtime. >>> I've got all of the groundwork laid to do this, but I'm having trouble with >>> access violations in my clones. >>> Since I'm *cloning* methods, they'll be generated into a class other than >>> the >>> one being cloned. But then since I'm cloning *methods*, they need to be >>> able to >>> access PRIVATE MEMBERS of the original instance. >>> I tried generating public bridge methods, but private types still break >>> that. If >>> possible, I'd like to just make my clone a "friend" of the original class >>> like >>> in C++, but I don't know how. >>> I fully control the classes that clones can be made from, so I can mark >>> anything >>> else as an "inner class" or "nestmate" as needed. I just can't figure out >>> what >>> each of those ALLOW on the JVM from the specification docs alone. And you >>> know >>> how helpful google is nowadays; I couldn't find anything no matter how I >>> phrased it. >>> Does anyone know how to do this? >> The class that encapsulates your clone should be an hidden class (this is the >> mechanism used to load lambda bodies) >> [ >> https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/invoke/MethodHandles.Lookup.html#defineHiddenClass(byte[],boolean,java.lang.invoke.MethodHandles.Lookup.ClassOption.. >> | >> https://docs.oracle.com/en/java/javase/25/docs/api/java.base/java/lang/invoke/MethodHandles.Lookup.html#defineHiddenClass(byte[],boolean,java.lang.invoke.MethodHandles.Lookup.ClassOption.. >> ] .) >>> Thank you so much for your help! >> regards, >> Rémi
