Step 1 - Mixin

mixin Auditable {
  late DateTime createdAt;
  DateTime? updatedAt;

  void initAudit() {
    createdAt = DateTime.now();
  }

  void touch() {
    updatedAt = DateTime.now();
  }
}

Step 2 - Apply to a model

class Task with Auditable {
  String title;

  Task(this.title) {
    initAudit();
  }

  void rename(String next) {
    title = next;
    touch();
  }
}

void main() {
  Task t = Task('learn mixins');
  print(t.createdAt);
  t.rename('learn Dart');
  print(t.updatedAt);
}

Step 3 - Optional constructor pattern

• If you prefer not to call initAudit() manually, use a factory or a small AuditableModel base class that calls it from an initializer list (tradeoffs apply).

Practice tasks

• Add Duration? get age => DateTime.now().difference(createdAt) as a getter on the mixin.
• Add a second type Note with Auditable and verify each instance has its own timestamps.
• Guard touch so it does nothing if title did not actually change (compare in rename).