combinedOrderedStringId function

String combinedOrderedStringId(List<String> ids, { String separator = '_', })

Generates an ordered ID from a list of unordered IDs, that can be used to identify the list of IDs.

For example, this can be used to combine user IDs into a single ID that represents the group of users.

Throws ArgumentError if:

• any ID is empty — ['', 'a'] and ['a'] would otherwise both look identifying but represent different inputs;
• any ID contains the separator (default _) — this would allow different inputs to produce the same combined ID (e.g. ['a', 'b_c'] and ['a_b', 'c']).

Implementation

String combinedOrderedStringId(
  List<String> ids, {
  String separator = '_',
}) {
  if (separator.isEmpty) {
    throw ArgumentError.value(separator, 'separator', 'must not be empty');
  }
  for (final id in ids) {
    if (id.isEmpty) {
      throw ArgumentError.value(id, 'ids', 'ID must not be empty');
    }
    if (id.contains(separator)) {
      throw ArgumentError.value(
        id,
        'ids',
        'ID must not contain the separator "$separator"',
      );
    }
  }
  final sorted = List.of(ids)..sort((a, b) => a.compareTo(b));
  return sorted.join(separator);
}