classes

main.dart

import 'dart:io';

class Logxy {
  static String sName;
  static num slog;
  static Logxy _logger;

  // Logxy._() : super._();

  // Logxy._(this.sName);

  factory Logxy() {
    print('Logger $slog');
    if (_logger == null) {
      slog = 1;
      print('Logger $slog');
      slog++;
      sName = 'xyz';
      _logger = Logxy.internal(); // Causes singleton instantiation
    }
    return _logger;
  }

  Logxy.internal();

  log(String msg) {
    print(msg);
  }
}

class MyClass {
  num instanceVar;
  static num start;
  static final MyClass _singleton = new MyClass._internal();

  factory MyClass(num startparam) {
    start = startparam;
    return _singleton;
  }

  MyClass._internal() {
    if (instanceVar == null) {
      instanceVar = start;
    } else {
      instanceVar++;
    }
    // initialization logic here
  }

  // rest of the class
}


class Beast  {
  void chase(Beast x) {
    print("Animal $x");
  }
}
class Animal extends Beast {
  void chase(Beast x) {
    print("Animal $x");
  }
}

class Mouse extends Animal {

}

class Cat  extends Beast {
  void chase(covariant Mouse x) {
    print("x: ${x}");
  }
}

main() {
  var c = Cat();
  var m = Mouse();
  c.chase(m);

  print(Platform.version);
// consuming code
  MyClass myObj1 = MyClass(1); // get back the singleton
  print('myObj1=${myObj1.instanceVar}');

// another piece of consuming code
  MyClass myObj2 = MyClass(2); // still getting back the singleton
  print('myObj2=${myObj2.instanceVar}');

  // Logxy logger1 = Logxy(); // Logger instantiation
  // logger1.log("Logger Instantiated ${Logxy.slog}");

  // Logxy logger2 = Logxy(); // Logger Object Re-use
  // logger2.log("Logger Object Re-used ${Logxy.slog}");
}