是否可以在Dart中使用默认的私有构造函数扩展类？

Question

Suppose that we have a class a :

class A {
  A._();
}

Its default constructor is private : A._() .

Is there any way to extends that class?

Problem

class B extends A {

}

This results in a compiler error :

The superclass 'A' doesn't have a zero argument constructor.

Trying to compose any constructor for B myself ( B() ) results in another error:

The superclass 'A' doesn't have an unnamed constructor.

Answer 1

No, there is no way. This is an effective way to prevent extending.

What you still can do is implementing the class.

class B implements A {}

If the class also has a public non-factory constructor, you can still extend it by forwarding the constructor call to such a named constructor of the super class.

class B extends A {
  B() : super.other();
}