extends_implements_with.dart

// library exception;

typedef VoidFunction = void Function();

class ExceptionOnMessage {
  final String message;
  const ExceptionOnMessage(this.message);
} 


abstract class Logger {
  void logException(Type t, [String? msg]) {
    print("TYPE ERROR $t: ${msg??msg}");
  }
  void doneLogging();
} 

void untrustworthy() {
  throw Exception("d");
}

void tryFunction(VoidFunction untrustworthy, Logger logger) {
  try {
    untrustworthy();
  } on ExceptionOnMessage catch (e) {
    logger.logException(e.runtimeType, e.message);
  } on Exception {
    print("EXCEPTION ERR");
    logger.logException(Exception);
  } finally {
    logger.doneLogging();
  }
}

class B {
  static late final int _n;
  

}

class A extends Logger implements B {
  @override
  void doneLogging() {
   _n = 1;
    // TODO: implement doneLogging
    print("DONE LOGGING, the value of n: $_n");
  }

  @override
  static late int _n;

}

void main(List<String> args) {
  final a = A();
  tryFunction(untrustworthy, a);
  print(a);
}

Extends, used to make instance and derive from a class. It's copy the content of super-class (derived class)

read more: https://medium.com/@manoelsrs/dart-extends-vs-implements-vs-with-b070f9637b36