what is the best way to attach a single object to multiple BlockEntities?

[sturdy ridge]

I'm trying to implement a multi-block struture of block entities. i encoutered one issue however, how to make is so all of those block entities have a reference to the same instance of shared-state object. I thought about saving it in all of the blocks and then do something along the lines of:

/// in Block Entity

MySharedStateInfo info = null; // all the data needed to create MySharedState
MySharedState state = null; // the actual shared state

@Override
public void readNbt(NbtCompound nbt) {
    super.readNbt(nbt);
    this.info = new MySharedStateInfo(nbt); 
    this.state = null;
}

MySharedState get() {
    if (state == null) {
        // duck interface over a basic concurent hash map in the world class
        WorldSharedStateView view = WorldSharedStateView.of(this.world);
  
        // wrapper over computeIfAbsent
        this.state = view.example_getOrCreateSharedState(this.pos, this.info);
    }

    return this.state;
}

so that only one instance is created, but idk if this is a good way to do this
it would require a lot of redundancy (saving the whole thing multiple times)
i thought about just saving the map in the World instance but i don't have experiance with doing that so i first thought about saving it just in the blocks

[maiden ravine]

One way to do it is to designate one of the blocks as controller and have it store the state. Sometimes this makes sense from a gameplay perspective, but sometime it might not work well.

You could also use PersistentState to store the data in world.

Another option, that might work especially well if you allow for arbitrary shapes for your multiblocks is using graphlib. With graphlib you can use a GraphEntity to store the state of the multiblock. However, graphlib isn't really well suited to fixed shape multiblocks