Function addExtraThingById

src/ui-solid/Provider.tsx:57–73

(
    thingOffset: Offset,
    id: Id,
    thing: ThingsByOffset[Offset],
  )

  );

  const addExtraThingById = <Offset extends Offsets>(
    thingOffset: Offset,
    id: Id,
    thing: ThingsByOffset[Offset],
  ): void => {
    setExtraThingsById((extraThingsById) =>
      objGet(
        extraThingsById[thingOffset] as IdObj<ThingsByOffset[Offset]>,
        id,
      ) == thing
        ? extraThingsById
        : (arrayWith(extraThingsById, thingOffset, {
            ...(extraThingsById[thingOffset] as IdObj<ThingsByOffset[Offset]>),
            [id]: thing,
          } as ThingsById<ThingsByOffset>[Offset]) as ExtraThingsById),
    );
  };

  const delExtraThingById = (thingOffset: Offsets, id: Id): void => {
    setExtraThingsById((extraThingsById) =>