SiwftUI Firebase modifying variable inside snapshot change not working - swift

Question

The following is a function to add a listener to a query. Whenever a document is added/removed I make some changes on two arrays (one of the user Ids and one of the user details). As you can see I tried printing everything: I correctly receive the data whenever it is added/removed, I can retrieve the document ID I need but whenever I append it to the usersReqestedUIDs array it always prints it as empty, even if I try to append a random string in it. Why is that?
func addRequestedUsersSnapshot() {
let db = Firestore.firestore()
let userRef = db.collection("user").document(user.UID)
let userRequestedRef = userRef.collection("friends").whereField("status", isEqualTo: "request")
// First query to fetch all friendIDs
userRequestedRef.addSnapshotListener { querySnapshot, error in
guard let snapshot = querySnapshot else {
print("Error fetching snapshots: (error!)")
return
}
snapshot.documentChanges.forEach { diff in
print("ids : (self.usersReqestedUIDs)")
print("type : (diff.type)")
if diff.type == .added {
print("doc id (diff.document.documentID)")
self.usersReqestedUIDs.append("hello")
print("added (diff.document.data())")
print("ids : (self.usersReqestedUIDs)")
self.fetchUserDetailsByUID(uid: diff.document.documentID) { result in
switch result {
case let .success(user):
self.usersReqestedDetails.append(user)
case let .failure(error):
print(error)
}
}
}
if diff.type == .removed {
print("removed (diff.document.data())")
self.usersReqestedDetails.removeAll(where: { $0.UID == diff.document.documentID })
self.usersReqestedUIDs.removeAll(where: { $0 == diff.document.documentID })
}
if diff.type == .modified {
print("modified (diff.document.data())")
}
}
}
}