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site</a></li></ul></li></ul></div></div><main id="page-content"><div id="site-toc--side" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry nav-item"><a class="nav-link" href="#lists">Lists</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#sets">Sets</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#maps">Maps</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#operators">Operators</a><ul class="nav"><li class="toc-entry nav-item"><a class="nav-link" href="#spread-operators">Spread operators</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#control-flow-operators">Control-flow operators</a></li></ul></li></ul></div><article><div class="content"><nav id="subnav"><ul><li class="previous"><a href="/language/records">⟨ Records</a></li><li class="next"><a href="/language/generics">Generics ⟩</a></li></ul></nav><div id="site-content-title"><h1>Collections</h1></div><div id="site-toc--inline" class="site-toc"><header class="site-toc__title">Contents</header><ul class="section-nav"><li class="toc-entry"><a href="#lists">Lists</a></li><li class="toc-entry"><a href="#sets">Sets</a></li><li class="toc-entry"><a href="#maps">Maps</a></li><li class="toc-entry"><a href="#operators">Operators</a><ul><li class="toc-entry"><a href="#spread-operators">Spread operators</a></li><li class="toc-entry"><a href="#control-flow-operators">Control-flow operators</a></li></ul></li></ul></div><p>Dart has built-in support for list, set, and map <a href="/libraries/dart-core#collections">collections</a>. To learn more about configuring the types collections contain, check out <a href="/language/generics">Generics</a>.</p><div class="header-wrapper"><h2 id="lists">Lists</h2><a class="heading-link" href="#lists" aria-label="Link to 'Lists' section">#</a></div><p>Perhaps the most common collection in nearly every programming language is the <em>array</em>, or ordered group of objects. In Dart, arrays are <a href="https://api.dart.dev/dart-core/List-class.html"><code>List</code></a> objects, so most people just call them <em>lists</em>.</p><p>Dart list literals are denoted by a comma separated list of expressions or values, enclosed in square brackets (<code>[]</code>). Here's a simple Dart list:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (list-literal)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> list = [</span><span style="color:#11796D">1</span><span style="color:#222222">, </span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">3</span><span style="color:#222222">];</span></span></code></pre></div></div><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>Dart infers that <code>list</code> has type <code>List<int></code>. If you try to add non-integer objects to this list, the analyzer or runtime raises an error. For more information, read about <a href="/language/type-system#type-inference">type inference</a>.</p></div></aside><p><a id="trailing-comma"></a> You can add a comma after the last item in a Dart collection literal. This <em>trailing comma</em> doesn't affect the collection, but it can help prevent copy-paste errors.</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (trailing-commas)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> list = [</span></span> <span class="line"><span style="color:#11796D"> 'Car'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'Boat'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'Plane'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222">];</span></span></code></pre></div></div><p>Lists use zero-based indexing, where 0 is the index of the first value and <code>list.length - 1</code> is the index of the last value. You can get a list's length using the <code>.length</code> property and access a list's values using the subscript operator (<code>[]</code>):</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (list-indexing)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> list = [</span><span style="color:#11796D">1</span><span style="color:#222222">, </span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">3</span><span style="color:#222222">];</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(list.length == </span><span style="color:#11796D">3</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(list[</span><span style="color:#11796D">1</span><span style="color:#222222">] == </span><span style="color:#11796D">2</span><span style="color:#222222">);</span></span> <span class="line"></span> <span class="line"><span style="color:#222222">list[</span><span style="color:#11796D">1</span><span style="color:#222222">] = </span><span style="color:#11796D">1</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(list[</span><span style="color:#11796D">1</span><span style="color:#222222">] == </span><span style="color:#11796D">1</span><span style="color:#222222">);</span></span></code></pre></div></div><p>To create a list that's a compile-time constant, add <code>const</code> before the list literal:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (const-list)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> constantList = </span><span style="color:#D43324">const</span><span style="color:#222222"> [</span><span style="color:#11796D">1</span><span style="color:#222222">, </span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">3</span><span style="color:#222222">];</span></span> <span class="line"><span style="color:#6E6E70">// constantList[1] = 1; // This line will cause an error.</span></span></code></pre></div></div><p>For more information about lists, refer to the Lists section of the <a href="/libraries/dart-core#lists"><code>dart:core</code> documentation</a>.</p><div class="header-wrapper"><h2 id="sets">Sets</h2><a class="heading-link" href="#sets" aria-label="Link to 'Sets' section">#</a></div><p>A set in Dart is an unordered collection of unique items. Dart support for sets is provided by set literals and the <a href="https://api.dart.dev/dart-core/Set-class.html"><code>Set</code></a> type.</p><p>Here is a simple Dart set, created using a set literal:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (set-literal)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> halogens = {</span><span style="color:#11796D">'fluorine'</span><span style="color:#222222">, </span><span style="color:#11796D">'chlorine'</span><span style="color:#222222">, </span><span style="color:#11796D">'bromine'</span><span style="color:#222222">, </span><span style="color:#11796D">'iodine'</span><span style="color:#222222">, </span><span style="color:#11796D">'astatine'</span><span style="color:#222222">};</span></span></code></pre></div></div><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>Dart infers that <code>halogens</code> has the type <code>Set<String></code>. If you try to add the wrong type of value to the set, the analyzer or runtime raises an error. For more information, read about <a href="/language/type-system#type-inference">type inference.</a></p></div></aside><p>To create an empty set, use <code>{}</code> preceded by a type argument, or assign <code>{}</code> to a variable of type <code>Set</code>:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (set-vs-map)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> names = <</span><span style="color:#0468D7">String</span><span style="color:#222222">>{};</span></span> <span class="line"><span style="color:#6E6E70">// Set<String> names = {}; // This works, too.</span></span> <span class="line"><span style="color:#6E6E70">// var names = {}; // Creates a map, not a set.</span></span></code></pre></div></div><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Set or map?</span></div><div class="alert-content"><p>The syntax for map literals is similar to that for set literals. Because map literals came first, <code>{}</code> defaults to the <code>Map</code> type. If you forget the type annotation on <code>{}</code> or the variable it's assigned to, then Dart creates an object of type <code>Map<dynamic, dynamic></code>.</p></div></aside><p>Add items to an existing set using the <code>add()</code> or <code>addAll()</code> methods:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (set-add-items)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> elements = <</span><span style="color:#0468D7">String</span><span style="color:#222222">>{};</span></span> <span class="line"><span style="color:#222222">elements.</span><span style="color:#6200EE">add</span><span style="color:#222222">(</span><span style="color:#11796D">'fluorine'</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#222222">elements.</span><span style="color:#6200EE">addAll</span><span style="color:#222222">(halogens);</span></span></code></pre></div></div><p>Use <code>.length</code> to get the number of items in the set:</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (set-length)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> elements = <</span><span style="color:#0468D7">String</span><span style="color:#222222">>{};</span></span> <span class="line"><span style="color:#222222">elements.</span><span style="color:#6200EE">add</span><span style="color:#222222">(</span><span style="color:#11796D">'fluorine'</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#222222">elements.</span><span style="color:#6200EE">addAll</span><span style="color:#222222">(halogens);</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(elements.length == </span><span style="color:#11796D">5</span><span style="color:#222222">);</span></span></code></pre></div></div><p>To create a set that's a compile-time constant, add <code>const</code> before the set literal:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (const-set)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">final</span><span style="color:#222222"> constantSet = </span><span style="color:#D43324">const</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#11796D"> 'fluorine'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'chlorine'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'bromine'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'iodine'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'astatine'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222">};</span></span> <span class="line"><span style="color:#6E6E70">// constantSet.add('helium'); // This line will cause an error.</span></span></code></pre></div></div><p>For more information about sets, refer to the Sets section of the <a href="/libraries/dart-core#sets"><code>dart:core</code> documentation</a>.</p><div class="header-wrapper"><h2 id="maps">Maps</h2><a class="heading-link" href="#maps" aria-label="Link to 'Maps' section">#</a></div><p>In general, a map is an object that associates keys and values. Both keys and values can be any type of object. Each <em>key</em> occurs only once, but you can use the same <em>value</em> multiple times. Dart support for maps is provided by map literals and the <a href="https://api.dart.dev/dart-core/Map-class.html"><code>Map</code></a> type.</p><p>Here are a couple of simple Dart maps, created using map literals:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (map-literal)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> gifts = {</span></span> <span class="line"><span style="color:#6E6E70"> // Key: Value</span></span> <span class="line"><span style="color:#11796D"> 'first'</span><span style="color:#222222">: </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'second'</span><span style="color:#222222">: </span><span style="color:#11796D">'turtledoves'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 'fifth'</span><span style="color:#222222">: </span><span style="color:#11796D">'golden rings'</span></span> <span class="line"><span style="color:#222222">};</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> nobleGases = {</span></span> <span class="line"><span style="color:#11796D"> 2</span><span style="color:#222222">: </span><span style="color:#11796D">'helium'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 10</span><span style="color:#222222">: </span><span style="color:#11796D">'neon'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 18</span><span style="color:#222222">: </span><span style="color:#11796D">'argon'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222">};</span></span></code></pre></div></div><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>Dart infers that <code>gifts</code> has the type <code>Map<String, String></code> and <code>nobleGases</code> has the type <code>Map<int, String></code>. If you try to add the wrong type of value to either map, the analyzer or runtime raises an error. For more information, read about <a href="/language/type-system#type-inference">type inference</a>.</p></div></aside><p>You can create the same objects using a Map constructor:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (map-constructor)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> gifts = </span><span style="color:#0468D7">Map</span><span style="color:#222222"><</span><span style="color:#0468D7">String</span><span style="color:#222222">, </span><span style="color:#0468D7">String</span><span style="color:#222222">>();</span></span> <span class="line"><span style="color:#222222">gifts[</span><span style="color:#11796D">'first'</span><span style="color:#222222">] = </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#222222">gifts[</span><span style="color:#11796D">'second'</span><span style="color:#222222">] = </span><span style="color:#11796D">'turtledoves'</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#222222">gifts[</span><span style="color:#11796D">'fifth'</span><span style="color:#222222">] = </span><span style="color:#11796D">'golden rings'</span><span style="color:#222222">;</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> nobleGases = </span><span style="color:#0468D7">Map</span><span style="color:#222222"><</span><span style="color:#0468D7">int</span><span style="color:#222222">, </span><span style="color:#0468D7">String</span><span style="color:#222222">>();</span></span> <span class="line"><span style="color:#222222">nobleGases[</span><span style="color:#11796D">2</span><span style="color:#222222">] = </span><span style="color:#11796D">'helium'</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#222222">nobleGases[</span><span style="color:#11796D">10</span><span style="color:#222222">] = </span><span style="color:#11796D">'neon'</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#222222">nobleGases[</span><span style="color:#11796D">18</span><span style="color:#222222">] = </span><span style="color:#11796D">'argon'</span><span style="color:#222222">;</span></span></code></pre></div></div><aside class="alert alert-info"><div class="alert-header"><i class="material-symbols" aria-hidden="true">info</i> <span>Note</span></div><div class="alert-content"><p>If you come from a language like C# or Java, you might expect to see <code>new Map()</code> instead of just <code>Map()</code>. In Dart, the <code>new</code> keyword is optional. For details, see <a href="/language/classes#using-constructors">Using constructors</a>.</p></div></aside><p>Add a new key-value pair to an existing map using the subscript assignment operator (<code>[]=</code>):</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (map-add-item)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> gifts = {</span><span style="color:#11796D">'first'</span><span style="color:#222222">: </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">};</span></span> <span class="line"><span style="color:#222222">gifts[</span><span style="color:#11796D">'fourth'</span><span style="color:#222222">] = </span><span style="color:#11796D">'calling birds'</span><span style="color:#222222">; </span><span style="color:#6E6E70">// Add a key-value pair</span></span></code></pre></div></div><p>Retrieve a value from a map using the subscript operator (<code>[]</code>):</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (map-retrieve-item)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> gifts = {</span><span style="color:#11796D">'first'</span><span style="color:#222222">: </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">};</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(gifts[</span><span style="color:#11796D">'first'</span><span style="color:#222222">] == </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">);</span></span></code></pre></div></div><p>If you look for a key that isn't in a map, you get <code>null</code> in return:</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (map-missing-key)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> gifts = {</span><span style="color:#11796D">'first'</span><span style="color:#222222">: </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">};</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(gifts[</span><span style="color:#11796D">'fifth'</span><span style="color:#222222">] == </span><span style="color:#11796D">null</span><span style="color:#222222">);</span></span></code></pre></div></div><p>Use <code>.length</code> to get the number of key-value pairs in the map:</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (map-length)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> gifts = {</span><span style="color:#11796D">'first'</span><span style="color:#222222">: </span><span style="color:#11796D">'partridge'</span><span style="color:#222222">};</span></span> <span class="line"><span style="color:#222222">gifts[</span><span style="color:#11796D">'fourth'</span><span style="color:#222222">] = </span><span style="color:#11796D">'calling birds'</span><span style="color:#222222">;</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(gifts.length == </span><span style="color:#11796D">2</span><span style="color:#222222">);</span></span></code></pre></div></div><p>To create a map that's a compile-time constant, add <code>const</code> before the map literal:</p> <?code-excerpt "misc/lib/language_tour/built_in_types.dart (const-map)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">final</span><span style="color:#222222"> constantMap = </span><span style="color:#D43324">const</span><span style="color:#222222"> {</span></span> <span class="line"><span style="color:#11796D"> 2</span><span style="color:#222222">: </span><span style="color:#11796D">'helium'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 10</span><span style="color:#222222">: </span><span style="color:#11796D">'neon'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#11796D"> 18</span><span style="color:#222222">: </span><span style="color:#11796D">'argon'</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222">};</span></span> <span class="line"></span> <span class="line"><span style="color:#6E6E70">// constantMap[2] = 'Helium'; // This line will cause an error.</span></span></code></pre></div></div><p>For more information about maps, refer to the Maps section of the <a href="/libraries/dart-core#maps"><code>dart:core</code> documentation</a>.</p><div class="header-wrapper"><h2 id="operators">Operators</h2><a class="heading-link" href="#operators" aria-label="Link to 'Operators' section">#</a></div><div class="header-wrapper"><h3 id="spread-operators">Spread operators</h3><a class="heading-link" href="#spread-operators" aria-label="Link to 'Spread operators' section">#</a></div><p>Dart supports the <strong>spread operator</strong> (<code>...</code>) and the <strong>null-aware spread operator</strong> (<code>...?</code>) in list, map, and set literals. Spread operators provide a concise way to insert multiple values into a collection.</p><p>For example, you can use the spread operator (<code>...</code>) to insert all the values of a list into another list:</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (list-spread)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> list = [</span><span style="color:#11796D">1</span><span style="color:#222222">, </span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">3</span><span style="color:#222222">];</span></span> <span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> list2 = [</span><span style="color:#11796D">0</span><span style="color:#222222">, ...list];</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(list2.length == </span><span style="color:#11796D">4</span><span style="color:#222222">);</span></span></code></pre></div></div><p>If the expression to the right of the spread operator might be null, you can avoid exceptions by using a null-aware spread operator (<code>...?</code>):</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (list-null-spread)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> list2 = [</span><span style="color:#11796D">0</span><span style="color:#222222">, ...?list];</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(list2.length == </span><span style="color:#11796D">1</span><span style="color:#222222">);</span></span></code></pre></div></div><p>For more details and examples of using the spread operator, see the <a href="https://github.com/dart-lang/language/blob/main/accepted/2.3/spread-collections/feature-specification.md">spread operator proposal.</a></p><p><a id="collection-operators"></a></p><div class="header-wrapper"><h3 id="control-flow-operators">Control-flow operators</h3><a class="heading-link" href="#control-flow-operators" aria-label="Link to 'Control-flow operators' section">#</a></div><p>Dart offers <strong>collection if</strong> and <strong>collection for</strong> for use in list, map, and set literals. You can use these operators to build collections using conditionals (<code>if</code>) and repetition (<code>for</code>).</p><p>Here's an example of using <strong>collection if</strong> to create a list with three or four items in it:</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (list-if)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> nav = [</span><span style="color:#11796D">'Home'</span><span style="color:#222222">, </span><span style="color:#11796D">'Furniture'</span><span style="color:#222222">, </span><span style="color:#11796D">'Plants'</span><span style="color:#222222">, </span><span style="color:#D43324">if</span><span style="color:#222222"> (promoActive) </span><span style="color:#11796D">'Outlet'</span><span style="color:#222222">];</span></span></code></pre></div></div><p>Dart also supports <a href="/language/branches#if-case">if-case</a> inside collection literals:</p><div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> nav = [</span><span style="color:#11796D">'Home'</span><span style="color:#222222">, </span><span style="color:#11796D">'Furniture'</span><span style="color:#222222">, </span><span style="color:#11796D">'Plants'</span><span style="color:#222222">, </span><span style="color:#D43324">if</span><span style="color:#222222"> (login </span><span style="color:#D43324">case</span><span style="color:#11796D"> 'Manager'</span><span style="color:#222222">) </span><span style="color:#11796D">'Inventory'</span><span style="color:#222222">];</span></span></code></pre></div></div><p>Here's an example of using <strong>collection for</strong> to manipulate the items of a list before adding them to another list:</p> <?code-excerpt "misc/test/language_tour/built_in_types_test.dart (list-for)"?> <div class="code-block-wrapper language-dart"><div class="code-block-body"><span class="code-block-language" title="Language dart">dart</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> listOfInts = [</span><span style="color:#11796D">1</span><span style="color:#222222">, </span><span style="color:#11796D">2</span><span style="color:#222222">, </span><span style="color:#11796D">3</span><span style="color:#222222">];</span></span> <span class="line"><span style="color:#D43324">var</span><span style="color:#222222"> listOfStrings = [</span><span style="color:#11796D">'#0'</span><span style="color:#222222">, </span><span style="color:#D43324">for</span><span style="color:#222222"> (</span><span style="color:#D43324">var</span><span style="color:#222222"> i </span><span style="color:#D43324">in</span><span style="color:#222222"> listOfInts) </span><span style="color:#11796D">'#</span><span style="color:#11796D">$</span><span style="color:#222222">i</span><span style="color:#11796D">'</span><span style="color:#222222">];</span></span> <span class="line"><span style="color:#D43324">assert</span><span style="color:#222222">(listOfStrings[</span><span style="color:#11796D">1</span><span style="color:#222222">] == </span><span style="color:#11796D">'#1'</span><span style="color:#222222">);</span></span></code></pre></div></div><p>For more details and examples of using collection <code>if</code> and <code>for</code>, see the <a href="https://github.com/dart-lang/language/blob/main/accepted/2.3/control-flow-collections/feature-specification.md">control flow collections proposal.</a></p><nav id="subnav"><ul><li class="previous"><a href="/language/records">⟨ Records</a></li><li class="next"><a href="/language/generics">Generics ⟩</a></li></ul></nav><p id="page-github-links"><span>Unless stated otherwise, the documentation on this site reflects Dart 3.5.4. 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