toBuilder for SuperBuilder

[Jan Rieke]

I recently investigated how we could add toBuilder support for SuperBuilder. Here is what I came up with:

    public static class Parent {
        private int field1;

        public static abstract class ParentBuilder<C extends Parent, B extends ParentBuilder<C, B>> {
            private int field1;
            protected B $fillValuesFrom(final C instance) {
                ParentBuilderImpl.$fillValuesFromInto(instance, this);
                return self();
            }
        }

        private static final class ParentBuilderImpl extends ParentBuilder<Parent, ParentBuilderImpl> {
            private static void $fillValuesFromInto(Parent instance, ParentBuilder<?,?> b) {
                b.field1(instance.field1);
            }
        }

        public ParentBuilder<?, ?> toBuilder() {
            return new ParentBuilderImpl().$fillValuesFrom(this);
        }
    }

    public static class Child extends Parent {
        private double field2;

        public static abstract class ChildBuilder<C extends Child, B extends ChildBuilder<C, B>> extends Parent.ParentBuilder<C, B> {
            private double field2;
            protected B $fillValuesFrom(final C instance) {
                super.$fillValuesFrom(instance);
                ChildBuilderImpl.$fillValuesFromInto(instance, this);
                return self();
            }
        }

        private static final class ChildBuilderImpl extends ChildBuilder<Child, ChildBuilderImpl> {
            private static void $fillValuesFromInto(Parent instance, ParentBuilder<?,?> b) {
                b.field2(instance.field2);
            }
        }

        public ChildBuilder<?, ?> toBuilder() {
            return new ChildBuilderImpl().$fillValuesFrom(this);
        }
    }

It's a bit ugly, because I need a method within both builder classes. The reason for that construction is that you cannot access instance.field1 from the abstract builder's $fillValuesFrom(), because C technically is an intersection class, which is not a nested class of the annotated type any more.

However, there are no type cast or other warnings on the code.

Could you live with that construction? Any other ideas?


[Reinier Zwitserloot]

Well, it's further than I got :)

Given that toBuilder is an optional thing, and given that I thought it wasn't possible _AT ALL_, I think this is going to have to be it. Perhaps a bunch of linters are going to choke on this but, hey, the fix to that is always to tell the linter tool not to lint lombok code.

[Jan Rieke]

Just to let you know: I'm currently working on a PR. It works quite good already, just some things to fix when there are generics on the annotated class.

[Reinier Zwitserloot]

Sounds good. We're close to another lombok release. Let's try to wait for this one. Unless that's a little too much pressure and you'd prefer it if we go ahead and start releasing without it.

[Jan Rieke]

I just created the PR: https://github.com/rzwitserloot/lombok/pull/1870

[Reinier Zwitserloot]

Thanks. I think this + doublechecks on JDK11 support and then we push out a version. Hopefulyl we can get to it next monday.

[Reinier Zwitserloot]

an earlier update to @Builder+@Singular to allow the collection to be 'null', whilst having toBuilder still work, is turning into this gigantic clusterball of a project.

I'm many hours in and nowhere near done, unfortunately.

[Jan Rieke]

Just let me know if I can assist somewhere.