CODEWITHSUNDEEP
dart
user1492051
user1492051

Reputation: 906

mixin whose super class is not Object

i want to do something like the following so bad

abstract class A{}                      
abstract class B extends A{}
abstract class C extends A{}
abstract class D extends B with C{} //C cannot be used as a mixin because it extends a class other than object

is there any solution other than copying the content of C in D?

the real names of my classes, to give you an idea of what i am trying to do

//A Observable
//B DynamicObservable
//C ObservableWithValidationErrors
//D DynamicObservableWithValidationErrors

Upvotes: 2

Views: 399

Answers (2)

Pixel Elephant
Pixel Elephant

Reputation: 21383

In some circumstances it might be possible to restructure your class to use multiple mixins instead:

abstract class Observable{}
abstract class Dynamic{}
abstract class ValidationErrors{}        
abstract class DynamicObservable extends Observable with Dynamic{}
abstract class ObservableWithValidationErrors extends Observable with ValidationErrors{}
abstract class DynamicObservableWithValidationErrors extends Observable with Dynamic, ValidationErrors{}

Of course, if Dynamic or ValidationErrors cannot be isolated this way, and rely on inheriting from Observable, this will not be possible.

Upvotes: 2

Alexandre Ardhuin
Alexandre Ardhuin

Reputation: 76243

There are some restrictions on the class you can use as mixin (See Mixins in Dart - Syntax and semantics).

However, in this proposal, a mixin may only be extracted from a class that obeys the following restrictions:

  1. The class has no declared constructors.
  2. The class’ superclass is Object.
  3. The class contains no super calls.

Those restrictions may be removed in the future.

The semantics are deliberately restricted in several ways, so as to reduce disruption to our existing implementations, while allowing future evolution toward a full-fledged mixin implementation. This restricted version already provides considerable value.

Upvotes: 3

Related Questions