Function hdk::link::delete_link

pub fn delete_link(add_link_header: HeaderHash) -> ExternResult<HeaderHash>

Delete a specific link creation element by its header.

Links are defined by a OR-Set CRDT of “Creates” and “Deletes”. The deletes form a “tombstone set”, each of which can nullify one of the creates. A link only “exists” if it has one or more “creates” which have not been nullified by a “delete”.

For this reason the delete references the header of the create. Even more than that, both creates and deletes are only headers, there is no separate entry and the delete is not simply a renamed mirror of the create (i.e. with base and target).

Consider what would happen if the system simply had “create link” and “delete link” pointing at the entry base and target without pairing:

• there would be no way to revert a specific link creation
• a delete may be intended for an create you haven’t seen yet, so network unpredictability would cause re-ording of any view on create/deletes which means an agent can see more deletes than creates, etc.
• there would only be two ways to summarise the state of a relationship between two entries, either “there are N more/less creates than deletes” or “there is at least one delete”, the former leads to flakiness as above and the latter means it would be impossible to create a link after any previous delete of any link. All of this is bad so link creates point to entries (See create_link ) and deletes point to creates.