Correct. Consider the following tree:
countries
+--france
| +--paris
+--spain
+--madrid
+--seville
That would be represented as follows in a Y.Map<string, Y.Array<string>> (using JSON syntax)
{
"__ROOTS__": ["countries"], // convenience entry for quickly finding root(s)
"countries": ["france", "spain"],
"france": ["paris"],
"paris": [],
"spain": ["madrid", "seville"],
"madrid": [],
"seville": [],
}
The problem of moving items doesn’t require a model this complex though. Let’s consider reordering in a simple list (Y.Array<string>):
["wash floors", "get milk", "homeschooling"]
Peer A moves "wash floors" to index 1, while Peer B moves "wash floors" to index 2. Since the move operation doesn’t exist, they both delete the "wash floors" element, then insert it at the new index. When these operations are merged we end up with "wash floors" twice in the list.
My question is - can this kind of conflict be resolved in Yjs? If not, would this be possible to add?
According to Martin Kleppmann, a CRDT move operation can be implementd with a combination of a List CRDT (Y.Array in the case of Yjs), an AWSet and a LWWRegister. I’d love to contribute this, but I think I need to learn a lot more about CRDTs and the Yjs codebase before I’d be able to.
Anyone more able than me?