dart with关键字

结论：
with 可以赋予类成员变量和方法，
不会覆盖原类的同名成员变量和方法
with 可以多个类，后面的类会覆盖前面的类

示例1：

class Mark{
  String name = "James with mark";
  void introduceSelf() {
    print(name);
  }
}
class Person with Mark {
}
void main() {
  Person().introduceSelf();
  print(Person().name);
}
输出:
James with mark
James with mark

从输出结果可以看出 Persion获得Mark的成员变量和方法

示例2：

class Mark{
  String name = "James with mark";
  void introduceSelf() {
    print(name);
  }
}
class Person with Mark {
  String name = "James";
  int age = 18;
  void introduceSelf() {
    print(name);
    print('I am $age years old');
  }
}
void main() {
  Person().introduceSelf();
}
输出
James
I am 18 years old

从输出结果可以看出,with 并没有覆盖掉Persion类的成员变量和方法，也就是说不会影响原有类的成员变量和方法。

示例3:

class Mark{
  String name = "James with mark";
  void introduceSelf() {
    print(name);
  }
}
class Person with Mark {
  String name = "James";
  int age = 18;
  // void introduceSelf() {
  //   print(name);
  //   print('I am $age years old');
  // }
}
void main() {
  Person().introduceSelf();
}
输出 
James

从输出结果可以看出，Persion通过with 获得了 Mark的 introduceSelf() 方法，并且成员变量name没有被覆盖。等同于如下：

class Person with Mark {
  String name = "James";
  int age = 18;
  void introduceSelf() {
    print(name);
  }
}

示例4：

class Mark{
  String name = "James with mark";
  void introduceSelf() {
    print(name);
  }
}
class MarkB{
  String name = "James with markb";
  void introduceSelf() {
    print(name);
  }
}
class Person with Mark ,MarkB{
}
class PersonB with MarkB,Mark{
}
void main() {
  Person().introduceSelf();
  print(Person().name);
  PersonB().introduceSelf();
  print(PersonB().name);
}
输出结果:
James with markb
James with markb
James with mark
James with mark

从输出结果可以看出,with 有先后顺序，后with的类会覆盖之前的。