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<!DOCTYPE html> <html lang="en"> <head> <meta charset="utf-8"> <meta http-equiv="X-UA-Compatible" content="IE=edge"> <meta name="viewport" content="width=device-width, height=device-height, initial-scale=1, user-scalable=no"> <meta name="description" content="dart:collection library API docs, for the Dart programming language."> <title>dart:collection library - Dart API</title> <link rel="canonical" href="https://api.dart.dev/dart-collection/dart-collection-library.html"> <link rel="preconnect" href="https://fonts.gstatic.com"> <link href="https://fonts.googleapis.com/css2?family=Roboto+Mono:ital,wght@0,300;0,400;0,500;0,700;1,400&display=swap" rel="stylesheet"> <link href="https://fonts.googleapis.com/css2?family=Material+Symbols+Outlined:opsz,wght,FILL,GRAD@24,400,0,0" rel="stylesheet"> <link rel="stylesheet" href="../static-assets/github.css?v1"> <link rel="stylesheet" href="../static-assets/styles.css?v1"> <link rel="icon" href="../static-assets/favicon.png?v1">  <script async src="https://www.googletagmanager.com/gtag/js?id=G-VVQ8908SJ5"></script> <script> window.dataLayer = window.dataLayer || []; function gtag(){dataLayer.push(arguments);} gtag('js', new Date()); gtag('config', 'G-VVQ8908SJ5'); </script> <link rel="preconnect" href="https://fonts.googleapis.com"> <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin> <link rel="preload" href="https://fonts.googleapis.com/css2?family=Google+Sans+Text:wght@400&family=Google+Sans:wght@500&display=swap" as="style"> <link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Google+Sans+Text:wght@400&family=Google+Sans:wght@500&display=swap"> <link rel="stylesheet" href="https://www.gstatic.com/glue/cookienotificationbar/cookienotificationbar.min.css"> </head> <body data-base-href="../" data-using-base-href="false" class="light-theme"> <div id="overlay-under-drawer"></div> <header id="title"> <span id="sidenav-left-toggle" class="material-symbols-outlined" role="button" tabindex="0">menu</span> <ol class="breadcrumbs gt-separated dark hidden-xs"> <li><a href="../index.html">Dart</a></li> <li class="self-crumb">dart:collection</li> </ol> <div class="self-name">dart:collection</div> <form class="search navbar-right" role="search"> <input type="text" id="search-box" autocomplete="off" disabled class="form-control typeahead" placeholder="Loading search..."> </form> <div class="toggle" id="theme-button" title="Toggle brightness"> <label for="theme"> <input type="checkbox" id="theme" value="light-theme"> <span id="dark-theme-button" class="material-symbols-outlined"> dark_mode </span> <span id="light-theme-button" class="material-symbols-outlined"> light_mode </span> </label> </div> </header> <main> <div id="dartdoc-main-content" class="main-content" data-above-sidebar="" data-below-sidebar="dart-collection/dart-collection-library-sidebar.html"> <div> <div id="external-links" class="btn-group"><a title="View source code" class="source-link" href="https://github.com/dart-lang/sdk/blob/88c9758ef131d430d8ce595c6bfb4c90574d3ddd/sdk/lib/collection/collection.dart#L55"><span class="material-symbols-outlined">description</span></a></div> <h1> <span class="kind-library">dart:collection</span> library </h1> </div> <section class="desc markdown"> <p>Classes and utilities that supplement the collection support in dart:core.</p> <p>To use this library in your code:</p> <pre class="language-dart"><code class="language-dart">import 'dart:collection'; </code></pre> <h2 id="map">Map</h2> <p>A finite mapping from unique keys to their associated values. Allows efficient lookup of the value associated with a key, if any, and iterating through the individual keys and values of the map. The <a href="../dart-core/Map-class.html">Map</a> interface has a number of implementations, including the following:</p> <ul> <li><a href="../dart-collection/HashMap-class.html">HashMap</a> is unordered, the order of iteration is not guaranteed.</li> <li><a href="../dart-collection/LinkedHashMap-class.html">LinkedHashMap</a> iterates in key insertion order.</li> <li><a href="../dart-collection/SplayTreeMap-class.html">SplayTreeMap</a> iterates the keys in sorted order.</li> <li><a href="../dart-collection/UnmodifiableMapView-class.html">UnmodifiableMapView</a> is a wrapper, an unmodifiable <a href="../dart-core/Map-class.html">Map</a> view of another <code>Map</code>.</li> </ul> <h2 id="set">Set</h2> <p>A collection of objects in which each object can occur only once. The <a href="../dart-core/Set-class.html">Set</a> interface has a number of implementations, including the following:</p> <ul> <li><a href="../dart-collection/HashSet-class.html">HashSet</a> does not guarantee the order of the objects in the iterations.</li> <li><a href="../dart-collection/LinkedHashSet-class.html">LinkedHashSet</a> iterates the objects in insertion order.</li> <li><a href="../dart-collection/SplayTreeSet-class.html">SplayTreeSet</a> iterates the objects in sorted order.</li> <li><a href="../dart-collection/UnmodifiableSetView-class.html">UnmodifiableSetView</a> is a wrapper, an unmodifiable <a href="../dart-core/Set-class.html">Set</a> view of another <code>Set</code>.</li> </ul> <h2 id="queue">Queue</h2> <p>A queue is a sequence of elements that is intended to be modified, by adding or removing elements, only at its ends. Dart queues are <em>double ended</em> queues, which means that they can be accessed equally from either end, and can therefore be used to implement both stack and queue behavior.</p> <ul> <li><a href="../dart-collection/Queue-class.html">Queue</a> is the general interface for queues.</li> <li><a href="../dart-collection/ListQueue-class.html">ListQueue</a> is a list-based queue. Default implementation for <a href="../dart-collection/Queue-class.html">Queue</a>.</li> <li><a href="../dart-collection/DoubleLinkedQueue-class.html">DoubleLinkedQueue</a> is a queue implementation based on a double-linked list.</li> </ul> <h2 id="list">List</h2> <p>An indexable sequence of objects. Objects can be accessed using their position, index, in the sequence. <a href="../dart-core/List-class.html">List</a> is also called an "array" in other programming languages.</p> <ul> <li><a href="../dart-collection/UnmodifiableListView-class.html">UnmodifiableListView</a> is a wrapper, an unmodifiable <a href="../dart-core/List-class.html">List</a> view of another <code>List</code>.</li> </ul> <h2 id="linkedlist">LinkedList</h2> <p><a href="../dart-collection/LinkedList-class.html">LinkedList</a> is a specialized double-linked list of elements that extends <a href="../dart-collection/LinkedListEntry-class.html">LinkedListEntry</a>. Each element knows its own place in the linked list, as well as which list it is in.</p> </section> <section class="summary offset-anchor" id="classes"> <h2>Classes</h2> <dl> <dt id="DoubleLinkedQueue"> <span class="name "><a href="../dart-collection/DoubleLinkedQueue-class.html">DoubleLinkedQueue</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> A <a href="../dart-collection/Queue-class.html">Queue</a> implementation based on a double-linked list. </dd> <dt id="DoubleLinkedQueueEntry"> <span class="name "><a href="../dart-collection/DoubleLinkedQueueEntry-class.html">DoubleLinkedQueueEntry</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> An entry in a doubly linked list. </dd> <dt id="HashMap"> <span class="name "><a href="../dart-collection/HashMap-class.html">HashMap</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> A hash-table based implementation of <a href="../dart-core/Map-class.html">Map</a>. </dd> <dt id="HashSet"> <span class="name "><a href="../dart-collection/HashSet-class.html">HashSet</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> An unordered hash-table based <a href="../dart-core/Set-class.html">Set</a> implementation. </dd> <dt id="HasNextIterator"> <span class="name deprecated"><a class="deprecated" href="../dart-collection/HasNextIterator-class.html">HasNextIterator</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> Wrapper for <a href="../dart-core/Iterator-class.html">Iterator</a> providing the pre-Dart 1.0 iterator interface. </dd> <dt id="LinkedHashMap"> <span class="name "><a href="../dart-collection/LinkedHashMap-class.html">LinkedHashMap</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> An insertion-ordered <a href="../dart-core/Map-class.html">Map</a> with expected constant-time lookup. </dd> <dt id="LinkedHashSet"> <span class="name "><a href="../dart-collection/LinkedHashSet-class.html">LinkedHashSet</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> A <a href="../dart-collection/LinkedHashSet-class.html">LinkedHashSet</a> is a hash-table based <a href="../dart-core/Set-class.html">Set</a> implementation. </dd> <dt id="LinkedList"> <span class="name "><a href="../dart-collection/LinkedList-class.html">LinkedList</a><span class="signature"><<wbr><span class="type-parameter">E extends <a href="../dart-collection/LinkedListEntry-class.html">LinkedListEntry</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span>></span></span> </dt> <dd> A specialized double-linked list of elements that extends <a href="../dart-collection/LinkedListEntry-class.html">LinkedListEntry</a>. </dd> <dt id="LinkedListEntry"> <span class="name "><a href="../dart-collection/LinkedListEntry-class.html">LinkedListEntry</a><span class="signature"><<wbr><span class="type-parameter">E extends <a href="../dart-collection/LinkedListEntry-class.html">LinkedListEntry</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span>></span></span> </dt> <dd> An object that can be an element in a <a href="../dart-collection/LinkedList-class.html">LinkedList</a>. </dd> <dt id="ListBase"> <span class="name "><a href="../dart-collection/ListBase-class.html">ListBase</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> Abstract implementation of a list. </dd> <dt id="ListQueue"> <span class="name "><a href="../dart-collection/ListQueue-class.html">ListQueue</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> List based <a href="../dart-collection/Queue-class.html">Queue</a>. </dd> <dt id="MapBase"> <span class="name "><a href="../dart-collection/MapBase-class.html">MapBase</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> Base class for implementing a <a href="../dart-core/Map-class.html">Map</a>. </dd> <dt id="MapView"> <span class="name "><a href="../dart-collection/MapView-class.html">MapView</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> Wrapper around a class that implements <a href="../dart-core/Map-class.html">Map</a> that only exposes <code>Map</code> members. </dd> <dt id="Queue"> <span class="name "><a href="../dart-collection/Queue-class.html">Queue</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> A <a href="../dart-collection/Queue-class.html">Queue</a> is a collection that can be manipulated at both ends. One can iterate over the elements of a queue through <a href="../dart-core/Iterable/forEach.html">forEach</a> or with an <a href="../dart-core/Iterator-class.html">Iterator</a>. </dd> <dt id="SetBase"> <span class="name "><a href="../dart-collection/SetBase-class.html">SetBase</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> Base implementation of <a href="../dart-core/Set-class.html">Set</a>. </dd> <dt id="SplayTreeMap"> <span class="name "><a href="../dart-collection/SplayTreeMap-class.html">SplayTreeMap</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> A <a href="../dart-core/Map-class.html">Map</a> of objects that can be ordered relative to each other. </dd> <dt id="SplayTreeSet"> <span class="name "><a href="../dart-collection/SplayTreeSet-class.html">SplayTreeSet</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> A <a href="../dart-core/Set-class.html">Set</a> of objects that can be ordered relative to each other. </dd> <dt id="UnmodifiableListView"> <span class="name "><a href="../dart-collection/UnmodifiableListView-class.html">UnmodifiableListView</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> An unmodifiable <a href="../dart-core/List-class.html">List</a> view of another List. </dd> <dt id="UnmodifiableMapBase"> <span class="name "><a href="../dart-collection/UnmodifiableMapBase-class.html">UnmodifiableMapBase</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> Basic implementation of an unmodifiable <a href="../dart-core/Map-class.html">Map</a>. </dd> <dt id="UnmodifiableMapView"> <span class="name "><a href="../dart-collection/UnmodifiableMapView-class.html">UnmodifiableMapView</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span></span> </dt> <dd> View of a <a href="../dart-core/Map-class.html">Map</a> that disallow modifying the map. </dd> <dt id="UnmodifiableSetView"> <span class="name "><a href="../dart-collection/UnmodifiableSetView-class.html">UnmodifiableSetView</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span></span> </dt> <dd> An unmodifiable <a href="../dart-core/Set-class.html">Set</a> view of another <a href="../dart-core/Set-class.html">Set</a>. </dd> </dl> </section> <section class="summary offset-anchor" id="extensions"> <h2>Extensions</h2> <dl> <dt id="IterableExtensions"> <span class="name "><a href="../dart-collection/IterableExtensions.html">IterableExtensions</a></span> on <a href="../dart-core/Iterable-class.html">Iterable</a><span class="signature"><<wbr><span class="type-parameter">T</span>></span> </dt> <dd> Operations on iterables. </dd> <dt id="NullableIterableExtensions"> <span class="name "><a href="../dart-collection/NullableIterableExtensions.html">NullableIterableExtensions</a></span> on <a href="../dart-core/Iterable-class.html">Iterable</a><span class="signature"><<wbr><span class="type-parameter">T?</span>></span> </dt> <dd> Operations on iterables with nullable elements. </dd> </dl> </section> <section class="summary offset-anchor" id="typedefs"> <h2>Typedefs</h2> <dl> <dt id="IterableBase" class=""> <span class="name"><a href="../dart-collection/IterableBase.html">IterableBase</a></span><<wbr><span class="type-parameter">E</span>> = <a href="../dart-core/Iterable-class.html">Iterable</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span> </span> </dt> <dd> Base class for implementing <a href="../dart-core/Iterable-class.html">Iterable</a>. </dd> <dt id="IterableMixin" class=""> <span class="name"><a href="../dart-collection/IterableMixin.html">IterableMixin</a></span><<wbr><span class="type-parameter">E</span>> = <a href="../dart-core/Iterable-class.html">Iterable</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span> </span> </dt> <dd> This <a href="../dart-core/Iterable-class.html">Iterable</a> mixin implements all <a href="../dart-core/Iterable-class.html">Iterable</a> members except <code>iterator</code>. </dd> <dt id="ListMixin" class=""> <span class="name"><a href="../dart-collection/ListMixin.html">ListMixin</a></span><<wbr><span class="type-parameter">E</span>> = <a href="../dart-collection/ListBase-class.html">ListBase</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span> </span> </dt> <dd> Base mixin implementation of a <a href="../dart-core/List-class.html">List</a> class. </dd> <dt id="MapMixin" class=""> <span class="name"><a href="../dart-collection/MapMixin.html">MapMixin</a></span><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>> = <a href="../dart-collection/MapBase-class.html">MapBase</a><span class="signature"><<wbr><span class="type-parameter">K</span>, <span class="type-parameter">V</span>></span> </span> </dt> <dd> Mixin implementing a <a href="../dart-core/Map-class.html">Map</a>. </dd> <dt id="SetMixin" class=""> <span class="name"><a href="../dart-collection/SetMixin.html">SetMixin</a></span><<wbr><span class="type-parameter">E</span>> = <a href="../dart-collection/SetBase-class.html">SetBase</a><span class="signature"><<wbr><span class="type-parameter">E</span>></span> </span> </dt> <dd> Mixin implementation of <a href="../dart-core/Set-class.html">Set</a>. </dd> </dl> </section> </div>  <div id="dartdoc-sidebar-left" class="sidebar sidebar-offcanvas-left">  <header id="header-search-sidebar" class="hidden-l"> <form class="search-sidebar" role="search"> <input type="text" id="search-sidebar" autocomplete="off" disabled class="form-control typeahead" placeholder="Loading search..."> </form> </header> <ol class="breadcrumbs gt-separated dark hidden-l" id="sidebar-nav"> 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