I would prefer dealing with this on the Serialize side. Is that doable without too much impact?

It should be possible, but I don't know if there is any impact yet.

I considered that approach, but the consumer should not need to be aware it is dealing with a proxy object. However, either way it is going to be ugly. It is either Serializer needs to know it is dealing with a proxy or the proxy needs to tell Serializer to skip certain properties. Then, there are third party serializers and proxy generators.

To me, the best way forward is to change LazyObjectInterface. Instead of doing:

$object->isLazyObjectInitialized();

we do this:

$object::isLazyObjectInitialized($object);

Alternatively, it should offer the option not to expose LazyObjectInterface. Similar to what Doctrine does, but with better DX.

WDYT?

Yes I agree, it'd be better to move all methods of LazyObjectInterface outside of it. We'd need a BC-path forward though.

Why adding the attribute on e.g. lazyObjectState while only isLazyObjectInitialized leaks?

I added them for completeness, because some serializers access private properties directly.

Thank you @priyadi.