关于Mixin和Dart类的继承

Question

Please look the code ,i want to know 1.who is C super 2.in the class C ,when i call 'super.method()', Mixin excute 'void method()'(so C's super is Mixin?), then, when excute 'super.method()', B excute 'void method()'(so C's super is B?),why?

It's running Dart 2.1.2

void main() {
  C().printSuper();
  C().method();
}

abstract class A {
  void method() {
    print("A");
  }
}

class B implements A {
  @override
  void method() {
    print("B");
  }
}

mixin Mixin on A {
  @override
  void method() {
    super.method();
    print("mixin");
  }
}

class C extends B with Mixin {
  void printSuper() {
    super.method();
  }
}



print message:

I/flutter (21340): B
I/flutter (21340): mixin
I/flutter (21340): B
I/flutter (21340): mixin

i expected the output print message:

I/flutter (21340): BI/flutter (21340): BI/flutter (21340): mixin

Answer 1

The superclass of C is B with Mixin , which is an anonymous class introduced by the extends B with Mixin clause.

The class C is equivalent to a class declared as follows:

class _BwithMixin extends B implements Mixin {
  void method() {
    super.method();
    print("mixin");
  }
}
class C extends _BwithMixin {
  void printSuper() {
    super.method();
  }
}

So, the printSuper doesn't directly hit the method of B , it hits the method of the superclass of C which is B with Mixin , and that method is the one copied from Mixin . It will then call super.method() from _BwithMixin , and the superclass of that is B , so it will first print mixin and then B .