/**
* Base class for various bits of metadata attached to a {@link MetadataShardDataTreeSnapshot}. This class is not
* an interface because we want to make sure all subclasses implement the externalizable proxy pattern, for which
/**
* Base class for various bits of metadata attached to a {@link MetadataShardDataTreeSnapshot}. This class is not
* an interface because we want to make sure all subclasses implement the externalizable proxy pattern, for which
* All concrete subclasses of this class should be final so as to form a distinct set of possible metadata. Since
* metadata is serialized along with {@link MetadataShardDataTreeSnapshot}, this set is part of the serialization format
* guarded by {@link PayloadVersion}.
*
* All concrete subclasses of this class should be final so as to form a distinct set of possible metadata. Since
* metadata is serialized along with {@link MetadataShardDataTreeSnapshot}, this set is part of the serialization format
* guarded by {@link PayloadVersion}.
*
*
* @return Externalizable proxy, may not be null
*/
protected abstract @Nonnull Externalizable externalizableProxy();
*
* @return Externalizable proxy, may not be null
*/
protected abstract @Nonnull Externalizable externalizableProxy();