remove
Remove key — and return the change: the tags currently on it, retired, and nothing else. Absorbing that patch drops the key; the retired tags stay witnessed, so the removal propagates on merge. To hold the resulting document locally, doc.piece(doc.remove(key)).
Concurrent writes of the same key on another replica survive the merge (add-wins): they mint a tag this removal never observed, so it is not in the delta's context.
Removing a key that is absent yields the lattice identity, so absorbing it changes nothing.
Throws
if the document was not configured with a replica id (i.e. it was deserialized and withReplica was not called beforehand).
Samples
val a = ReplicaId("A")
val b = ReplicaId("B")
fun text(writer: ReplicaId, value: String) =
JsonNode.Leaf(MVRegister.empty<JsonValue>().set(writer, JsonValue.Str(value)))
// Two peers have converged on a document with a title and a long body.
var alpha = JsonCrdt.empty(a)
.piece { it.set("title", text(a, "Draft")) }
.piece { it.set("body", text(a, "a very long document body")) }
var bravo = alpha.withReplica(b)
// B retitles the document and puts only that key on the wire. The body does not travel —
// that is the whole saving, and it holds however large the rest of the document gets.
val retitle = bravo.set("title", text(b, "Final"))
check(retitle.delta.keys == setOf("title"))
check(retitle.delta["body"] == null)
alpha = alpha.piece(retitle)
bravo = bravo.piece(retitle)
check(alpha == bravo)
// Both scalar writes are retained, because neither observed the other: the leaf is a
// multi-value register the caller resolves by writing again once it has read both.
val title = alpha["title"] as JsonNode.Leaf
check(title.register.values == setOf(JsonValue.Str("Draft"), JsonValue.Str("Final")))
// A concurrent write beats a concurrent remove: B's write mints a tag A's remove never saw.
val concurrent = alpha.withReplica(b).set("title", text(b, "Revived"))
check("title" in alpha.piece(alpha.remove("title")).piece(concurrent).keys)
// A remove ships the retired tags and nothing else — its delta holds no key at all.
val drop = alpha.remove("body")
check(drop.delta.keys.isEmpty())
alpha = alpha.piece(drop)
bravo = bravo.piece(drop)
check("body" !in alpha.keys)
check("body" !in bravo.keys)Content copied to clipboard