011_classes copy.dart

import 'dart:math';

class Point {
  double x, y;
  Point(this.x, this.y);

  static double distanceBetween(Point a, Point b) {
    var dx = a.x - b.x;
    var dy = a.y - b.y;
    return sqrt(dx * dx + dy * dy);
  }
}

class Person {
  final String _name;

  Person(this._name);

  String greet(String who) => 'Hello, $who. I am $_name.';
}

// An implementation of the Person interface.
class Impostor implements Person {
  String get _name => '';

  String greet(String who) => 'Hi $who. Do you know who I am?';
}

String greetBob(Person person) => person.greet('Bob');

void foo1() {
  var a = Point(2, 2);
  var b = Point(4, 4);
  var distance = Point.distanceBetween(a, b);
  assert(2.8 < distance && distance < 2.9);
  print(distance);
}

class ProfileMark {
  final String name;
  final DateTime start = DateTime.now();

  ProfileMark(this.name);
  ProfileMark.unnamed() : name = '';
}

void foo2() {
  print(greetBob(Person('Kathy')));
  print(greetBob(Impostor()));
}

void main(List<String> args) {
  foo2();
}