Constructor with not initialized final class variables

Question

I have this class:

class Entry {
  final String id;
  final List<ListEntry> listEntries;

  Entry({this.listEntries}):
        id = Uuid().v4();

  Entry.withId({this.id, this.listEntries});
}
// create new class instance
var e = Entry();

Now when I call any method on e.listEntries I will get a NPE because it is not initialized. Is there a way to have it default to an empty list in case the constructor argument is not provided?

Answer 1

You can use a Factory constructor:

class Entry {
  final String id;
  final List<String> listEntries;

  factory Entry({List<String> listEntries}) {
    return Entry._(listEntries ?? []);
  }

  Entry._(this.listEntries):
        id = Uuid().v4();

  Entry.withId({this.id, this.listEntries});
}