How do I extend a List in Dart?

Question

I want to create a more specialized list in dart. I can't directly extend List. What are my options?

Answer 1

To make a class implement List there are several ways :

• Extending ListBase and implementing length, operator[], operator[]= and length= :

import 'dart:collection';  class MyCustomList<E> extends ListBase<E> {   final List<E> l = [];   MyCustomList();    void set length(int newLength) { l.length = newLength; }   int get length => l.length;   E operator [](int index) => l[index];   void operator []=(int index, E value) { l[index] = value; }    // your custom methods } 

• Mixin ListMixin and implementing length, operator[], operator[]= and length= :

import 'dart:collection';  class MyCustomList<E> extends Base with ListMixin<E> {   final List<E> l = [];   MyCustomList();    void set length(int newLength) { l.length = newLength; }   int get length => l.length;   E operator [](int index) => l[index];   void operator []=(int index, E value) { l[index] = value; }    // your custom methods } 

• Delegating to an other List with DelegatingList from the quiver package:

import 'package:quiver/collection.dart';  class MyCustomList<E> extends DelegatingList<E> {   final List<E> _l = [];    List<E> get delegate => _l;    // your custom methods } 

• Delegating to an other List with DelegatingList from the collection package:

import 'package:collection/wrappers.dart';  class MyCustomList<E> extends DelegatingList<E> {   final List<E> _l;    MyCustomList() : this._(<E>[]);   MyCustomList._(l) :     _l = l,     super(l);    // your custom methods } 

Depending on your code each of those options has their advantages. If you wrap/delegate an existing list you should use the last option. Otherwise, use one of the two first options depending on your type hierarchy (mixin allowing to extend another Object).