Identical Items List

Introduction

The package identical_items_list provides a non-empty unmodifiable Dart list containing identical items. An object of type IdenticalItemsList is unmodifiable in the sense that methods changing the list-length or its elements throw an UnsupportedError.

Use Case

Consider a function that returns a (potentially very long) list. If the list contains identical entries for a certain case, it might be more efficient to return an IdenticalItemsList instead of creating and returning a standard List object:

final list = List.filled(1000000, 42); // 14000 microseconds
final iList = IdenticalItemsList(value: 42, length: 1000000); // 0.02 microseconds

For more details see the page showing benchmark scores.

Usage

To use this library include identical_items_list as a dependency in your pubspec.yaml file. The example below shows how to construct an object of type IdenticalItemsList:

import 'package:identical_items_list/identical_items_list.dart';

void main(List<String> args) {
  final list = IdenticalItemsList(value: 42, length: 1000000);

  print('List: $list \n');

  print('Type: list is List<int>: ${list is List<int>} \n');

  print('Length:  ${list.length} \n');

  final sum = list.reduce((previousValue, item) => previousValue + item);
  print('Sum: $sum \n');

  print('Access: list[1024] = ${list[1024]}');
}

$ dart example/bin/example.dart
List: [42, 42, 42, 42, 42, ..., 42, 42]

Type: is List<int>: true

Length: 1000000

Sum: 42000000

Access: list[1024] = 42

Notes

• It is not possible to create an empty IdenticalItemsList. The constructor parameter value is required and the default list length is one.

• The class IdenticalItemsList provides a const constructor making it possible to define const objects:

  final list1 = const IdenticalItemsList(value: 42, length: 1000);
  final list2 = const IdenticalItemsList(value: 42, length: 1000);
  
  print(list1 == list2); // true
  print(identical(list1 == list2)); // true
  

• An object of type IdenticalItemsList<T> is immutable if the constructor parameter value is an immutable object.

Examples

For further information see example.

Features and bugs

Please file feature requests and bugs at the issue tracker.