ios – What’s the syntax for this closure for fetchDatabaseChangesResultBlock?

iOS Cloudkit FetchDatabaseChangesOperation() has a closure block outlined as:

fetchDatabaseChangesResultBlock: ((_ operationResult:
    End result<(serverChangeToken: CKServerChangeToken, moreComing: Bool), Error>) -> Void)?

My query is, what does an precise closure block appear to be?

For instance, I attempted this, which compiles:

let operation = CKFetchDatabaseChangesOperation(previousServerChangeToken: changeToken)

operation.fetchDatabaseChangesResultBlock = {
    lead to
}

In must get the serverChangeToken, the moreComing worth, and the Error. However I can not work out what “outcome” is, or even when I’ve the fitting signature.

Any assist could be appreciated! I can not determine this one out.