main.dart

class Comparable {
  final String content;
  
  Comparable(this.content);
  
  @override
  bool operator ==(other) {
    print('==');
    return other is Comparable && other.hashCode == hashCode;
  }
  
  @override
  int get hashCode {
    print('get hashCode');
    return content.hashCode;
  }
}

void main() {
  final a = <Comparable>{ Comparable('a'), Comparable('b'), Comparable('a') };
  print(a.length);
}