addAll method
Add all values
to the set. If the set was modified, it is persisted
immediately.
If values
is empty or all values are already present, no write occurs.
This method is more efficient than calling add repeatedly.
Implementation
Future<void> addAll(Iterable<T> values) async {
final before = _mem.length;
_mem.addAll(values);
if (_mem.length != before) await _persist();
}