Validating unique prop value within array?

[RoxKilly]

Suppose I have an array of messages with field id. How can I validate uniqueness within the array?

message Student {
  string id = 1;
}

message Class {
  repeated Student students = 1; // Possible to validate unique ids?
}

[RoxKilly]

Cross-posted in protovalidate (just discovered it). Feel free to close this if that project is likely the better place to solve this problem.

[rodaine]

Correct, this is not possible in PGV, but can likely be handled via a CEL expression in protovalidate.