Dart view of a list with a map function

mapped_list_view.dart

import 'dart:collection';

abstract class MappedListView<T, R> implements List<R> {
  factory MappedListView(
    List<T> wrapped,
    R Function(T element) mapper,
  ) = _MappedListView<T, R>;
}

class _MappedListView<T, R> with ListMixin<R> implements List<R>, MappedListView<T, R> {
  _MappedListView(
    this.wrapped,
    this.mapper,
  );

  final List<T> wrapped;
  final R Function(T element) mapper;

  @override
  int get length => wrapped.length;

  @override
  set length(int value) => wrapped.length = value;

  @override
  R operator [](int index) {
    return mapper(wrapped[index]);
  }

  @override
  void operator []=(int index, R value) {
    throw UnsupportedError('Assigning to a MappedListView is not supported');
  }
}