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aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-2-10"><li class="nav-item"><a class="nav-link" href="/libraries/async/async-await"><div><span>Tutorial</span></div></a></li><li class="nav-item"><a class="nav-link" href="/libraries/async/futures-error-handling"><div><span>Futures and error handling</span></div></a></li><li class="nav-item"><a class="nav-link" href="/libraries/async/using-streams"><div><span>Using streams</span></div></a></li><li class="nav-item"><a class="nav-link" href="/libraries/async/creating-streams"><div><span>Creating streams</span></div></a></li></ul></li></ul></li><li class="nav-item"><button class="nav-link collapsed collapsible" data-toggle="collapse" data-target="#-sidenav-3" role="button" aria-expanded="false" aria-controls="-sidenav-3"><span>Effective Dart</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-3"><li class="nav-item"><a class="nav-link" href="/effective-dart"><div><span>Overview</span></div></a></li><li class="nav-item"><a class="nav-link" href="/effective-dart/style"><div><span>Style</span></div></a></li><li class="nav-item"><a class="nav-link" href="/effective-dart/documentation"><div><span>Documentation</span></div></a></li><li class="nav-item"><a class="nav-link" href="/effective-dart/usage"><div><span>Usage</span></div></a></li><li class="nav-item"><a class="nav-link" href="/effective-dart/design"><div><span>Design</span></div></a></li></ul></li><li class="nav-item"><button class="nav-link active collapsible" data-toggle="collapse" data-target="#-sidenav-4" role="button" aria-expanded="true" aria-controls="-sidenav-4"><span>Packages</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse show" id="-sidenav-4"><li class="nav-item"><a class="nav-link" href="/tools/pub/packages"><div><span>How to use packages</span></div></a></li><li class="nav-item"><a class="nav-link" href="/resources/useful-packages"><div><span>Commonly used packages</span></div></a></li><li class="nav-item"><a class="nav-link active" href="/tools/pub/create-packages"><div><span>Creating packages</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/publishing"><div><span>Publishing packages</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/writing-package-pages"><div><span>Writing package pages</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/workspaces"><div><span>Workspaces (monorepo support)</span></div></a></li><li class="nav-item"><button class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#-sidenav-4-7" role="button" aria-expanded="false" aria-controls="-sidenav-4-7"><span>Package reference</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-4-7"><li class="nav-item"><a class="nav-link" href="/tools/pub/dependencies"><div><span>Dependencies</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/glossary"><div><span>Glossary</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/package-layout"><div><span>Package layout conventions</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/environment-variables"><div><span>Pub environment variables</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/pubspec"><div><span>Pubspec file</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/troubleshoot"><div><span>Troubleshooting pub</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/verified-publishers"><div><span>Verified publishers</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tools/pub/security-advisories"><div><span>Security advisories</span></div></a></li><li 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representation</span></div></a></li><li class="nav-item"><a class="nav-link" href="/resources/google-apis"><div><span>Google APIs</span></div></a></li><li class="nav-item"><a class="nav-link" href="/multiplatform-apps"><div><span>Multi-platform apps</span></div></a></li><li class="nav-item"><button class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#-sidenav-5-5" role="button" aria-expanded="false" aria-controls="-sidenav-5-5"><span>Command-line & server apps</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-5-5"><li class="nav-item"><a class="nav-link" href="/server"><div><span>Overview</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tutorials/server/get-started"><div><span>Get started</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tutorials/server/cmdline"><div><span>Write command-line apps</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tutorials/server/fetch-data"><div><span>Fetch data from the internet</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tutorials/server/httpserver"><div><span>Write HTTP servers</span></div></a></li><li class="nav-item"><a class="nav-link" href="/server/libraries"><div><span>Libraries & packages</span></div></a></li><li class="nav-item"><a class="nav-link" href="/server/google-cloud"><div><span>Google Cloud</span></div></a></li></ul></li><li class="nav-item"><button class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#-sidenav-5-6" role="button" aria-expanded="false" aria-controls="-sidenav-5-6"><span>Web apps</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-5-6"><li class="nav-item"><a class="nav-link" href="/web"><div><span>Overview</span></div></a></li><li class="nav-item"><a class="nav-link" href="/web/get-started"><div><span>Get started</span></div></a></li><li class="nav-item"><a class="nav-link" href="/web/deployment"><div><span>Deployment</span></div></a></li><li class="nav-item"><a class="nav-link" href="/web/libraries"><div><span>Libraries & packages</span></div></a></li><li class="nav-item"><a class="nav-link" href="/web/wasm"><div><span>Wasm compilation</span></div></a></li></ul></li><li class="nav-item"><a class="nav-link" href="/libraries/core/environment-declarations"><div><span>Environment declarations</span></div></a></li></ul></li><li class="nav-item"><button class="nav-link collapsed collapsible" data-toggle="collapse" data-target="#-sidenav-6" role="button" aria-expanded="false" aria-controls="-sidenav-6"><span>Interoperability</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-6"><li class="nav-item"><a class="nav-link" href="/interop/c-interop"><div><span>C interop</span></div></a></li><li class="nav-item"><a class="nav-link" href="/interop/objective-c-interop"><div><span>Objective-C & Swift interop</span></div></a></li><li class="nav-item"><a class="nav-link" href="/interop/java-interop"><div><span>Java & Kotlin interop</span></div></a></li><li class="nav-item"><button class="nav-link collapsible collapsed" data-toggle="collapse" data-target="#-sidenav-6-4" role="button" aria-expanded="false" aria-controls="-sidenav-6-4"><span>JavaScript interop</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-6-4"><li class="nav-item"><a class="nav-link" href="/interop/js-interop"><div><span>Overview</span></div></a></li><li class="nav-item"><a class="nav-link" href="/interop/js-interop/usage"><div><span>Usage</span></div></a></li><li class="nav-item"><a class="nav-link" href="/interop/js-interop/js-types"><div><span>JS types</span></div></a></li><li class="nav-item"><a class="nav-link" 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aria-hidden="true">expand_more</span></button><ul class="nav collapse" id="-sidenav-9-6"><li class="nav-item"><a class="nav-link" href="/resources/coming-from/js-to-dart"><div><span>JavaScript to Dart</span></div></a></li><li class="nav-item"><a class="nav-link" href="/resources/coming-from/swift-to-dart"><div><span>Swift to Dart</span></div></a></li></ul></li><div class="sidenav-divider"></div><li class="nav-item"><a class="nav-link" href="/resources/faq"><div><span>FAQ</span></div></a></li><li class="nav-item"><a class="nav-link" href="/resources/glossary"><div><span>Glossary</span></div></a></li><li class="nav-item"><a class="nav-link" href="/resources/books"><div><span>Books</span></div></a></li><li class="nav-item"><a class="nav-link" href="/resources/videos"><div><span>Videos</span></div></a></li><li class="nav-item"><a class="nav-link" href="/tutorials"><div><span>Tutorials</span></div></a></li></ul></li><li class="nav-item"><button class="nav-link collapsible" data-toggle="collapse" data-target="#-sidenav-10" role="button" aria-expanded="true" aria-controls="-sidenav-10"><span>Related sites</span> <span class="material-symbols expander" aria-hidden="true">expand_more</span></button><ul class="nav collapse show" id="-sidenav-10"><li class="nav-item"><a class="nav-link" href="https://api.dart.dev" target="_blank" rel="noopener"><div><span>API reference</span><span class="material-symbols" aria-hidden="true">open_in_new</span></div></a></li><li class="nav-item"><a class="nav-link" href="https://medium.com/dartlang" target="_blank" rel="noopener"><div><span>Blog</span><span class="material-symbols" aria-hidden="true">open_in_new</span></div></a></li><li class="nav-item"><a class="nav-link" href="https://dartpad.dev" target="_blank" rel="noopener"><div><span>DartPad (online editor)</span><span class="material-symbols" aria-hidden="true">open_in_new</span></div></a></li><li class="nav-item"><a class="nav-link" href="https://flutter.dev" target="_blank" rel="noopener"><div><span>Flutter</span><span class="material-symbols" aria-hidden="true">open_in_new</span></div></a></li><li class="nav-item"><a class="nav-link" href="https://pub.dev" target="_blank" rel="noopener"><div><span>Package site</span><span class="material-symbols" aria-hidden="true">open_in_new</span></div></a></li></ul></li></ul></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="#creating-a-new-package">Creating a new package</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#what-makes-a-package">What makes a package</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#organizing-a-package">Organizing a package</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#importing-library-files">Importing library files</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#conditionally-importing-and-exporting-library-files">Conditionally importing and exporting library files</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#providing-additional-files">Providing additional files</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#documenting-a-library">Documenting a library</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#distributing-a-library">Distributing an open source library</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#resources">Resources</a></li></ul></div><article><div class="content"><div id="site-content-title"><h1>Creating packages</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="#creating-a-new-package">Creating a new package</a></li><li class="toc-entry"><a href="#what-makes-a-package">What makes a package</a></li><li class="toc-entry"><a href="#organizing-a-package">Organizing a package</a></li><li class="toc-entry"><a href="#importing-library-files">Importing library files</a></li><li class="toc-entry"><a href="#conditionally-importing-and-exporting-library-files">Conditionally importing and exporting library files</a></li><li class="toc-entry"><a href="#providing-additional-files">Providing additional files</a></li><li class="toc-entry"><a href="#documenting-a-library">Documenting a library</a></li><li class="toc-entry"><a href="#distributing-a-library">Distributing an open source library</a></li><li class="toc-entry"><a href="#resources">Resources</a></li></ul></div><p>The Dart ecosystem uses <a href="/tools/pub/packages">packages</a> to share software such as libraries and tools. This page tells you how to create a standard shared <a href="/tools/pub/glossary#package">package</a>.</p><div class="header-wrapper"><h2 id="creating-a-new-package">Creating a new package</h2><a class="heading-link" href="#creating-a-new-package" aria-label="Link to 'Creating a new package' section">#</a></div><p>To create the initial directory and structure for a package, use the <a href="/tools/dart-create"><code>dart create</code></a> command and the <code>package</code> template:</p><div class="code-block-wrapper language-console"><div class="code-block-body"><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#222222">$ dart create -t package <PACKAGE_NAME></span></span></code></pre></div></div><div class="header-wrapper"><h2 id="what-makes-a-package">What makes a package</h2><a class="heading-link" href="#what-makes-a-package" aria-label="Link to 'What makes a package' section">#</a></div><p>The following diagram shows the simplest layout of a package:</p><p><img src="/assets/img/libraries/simple-lib2.png" alt="root directory contains pubspec.yaml and lib/file.dart"></p><p>The minimal requirements for a library are:</p><dl><dt>pubspec file</dt><dd>The <code>pubspec.yaml</code> file for a library is the same as for an <a href="/tools/pub/glossary#application-package">application package</a>—there is no special designation to indicate that the package is a library.</dd><dt>lib directory</dt><dd>As you might expect, the library code lives under the <em>lib</em> directory and is public to other packages. You can create any hierarchy under lib, as needed. By convention, implementation code is placed under <em>lib/src</em>. Code under lib/src is considered private; other packages should never need to import <code>src/...</code>. To make APIs under lib/src public, you can export lib/src files from a file that's directly under lib.</dd></dl><div class="header-wrapper"><h2 id="organizing-a-package">Organizing a package</h2><a class="heading-link" href="#organizing-a-package" aria-label="Link to 'Organizing a package' section">#</a></div><p>Packages are easiest to maintain, extend, and test when you create small, individual libraries, referred to as <em>mini libraries</em>. In most cases, each class should be in its own mini library, unless you have a situation where two classes are tightly coupled.</p><aside class="alert alert-info"><div class="alert-header"><span class="material-symbols" aria-hidden="true">info</span> <span>Note</span></div><div class="alert-content"><p>You might know about the <code>part</code> directive. This directive allows you to split a library into multiple Dart files. Though part files can incorporate generated code into a library, the Dart team doesn't recommend using them. Instead, create small libraries.</p></div></aside><p>Create a "main" library file directly under lib, lib/<em><package-name></em>.dart, that exports all of the public APIs. This allows the user to get all of a library's functionality by importing a single file.</p><p>The lib directory might also include other importable, non-src, libraries. For example, perhaps your main library works across platforms, but you create separate libraries that rely on <code>dart:io</code> or <code>dart:js_interop</code>. Some packages have separate libraries that are meant to be imported with a prefix, when the main library is not.</p><p>Let's look at the organization of a real-world package: shelf. The <a href="https://github.com/dart-lang/shelf">shelf</a> package provides an easy way to create web servers using Dart, and is laid out in a structure that is commonly used for Dart packages:</p><p><img src="/assets/img/libraries/shelf.png" alt="shelf root directory contains example, lib, test, and tool subdirectories"></p><p>Directly under lib, the main library file, <code>shelf.dart</code>, exports API from several files in <code>lib/src</code>. To avoid exposing more API than intended—and to give developers an overview of the entire public API of the package—<code>shelf.dart</code> uses <code>show</code> to specify exactly which symbols to export:</p><div class="code-block-wrapper language-dart"><div class="code-block-header">lib/shelf.dart</div><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">export</span><span style="color:#11796D"> 'src/cascade.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Cascade;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/handler.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Handler;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/hijack_exception.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> HijackException;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/middleware.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Middleware, createMiddleware;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/middleware/add_chunked_encoding.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> addChunkedEncoding;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/middleware/logger.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> logRequests;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/middleware_extensions.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> MiddlewareExtensions;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/pipeline.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Pipeline;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/request.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Request;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/response.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Response;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/server.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> Server;</span></span> <span class="line"><span style="color:#D43324">export</span><span style="color:#11796D"> 'src/server_handler.dart'</span><span style="color:#D43324"> show</span><span style="color:#222222"> ServerHandler;</span></span></code></pre></div></div><p>The shelf package also contains a mini library: shelf_io. This adapter handles HttpRequest objects from <code>dart:io</code>.</p><aside class="alert alert-success"><div class="alert-header"><span class="material-symbols" aria-hidden="true">lightbulb</span> <span>Tip</span></div><div class="alert-content"><p>For the best performance when developing with the development JavaScript compiler through <a href="/tools/webdev#serve"><code>webdev serve</code></a>, put <a href="/tools/pub/package-layout#implementation-files">implementation files</a> under <code>/lib/src</code>, instead of elsewhere under <code>/lib</code>. Also, avoid imports of <code>package:<em>package_name</em>/src/...</code>.</p></div></aside><div class="header-wrapper"><h2 id="importing-library-files">Importing library files</h2><a class="heading-link" href="#importing-library-files" aria-label="Link to 'Importing library files' section">#</a></div><p>When importing a library file from another package, use the <code>package:</code> directive to specify the URI of that file.</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">import</span><span style="color:#11796D"> 'package:utilities/utilities.dart'</span><span style="color:#222222">;</span></span></code></pre></div></div><p>When importing a library file from your own package, use a relative path when both files are inside of lib, or when both files are outside of lib. Use <code>package:</code> when the imported file is in lib and the importer is outside.</p><p>The following graphic shows how to import <code>lib/foo/a.dart</code> from both lib and web.</p><p><img src="/assets/img/libraries/import-lib-rules.png" alt="lib/bar/b.dart uses a relative import; web/main.dart uses a package import"></p><div class="header-wrapper"><h2 id="conditionally-importing-and-exporting-library-files">Conditionally importing and exporting library files</h2><a class="heading-link" href="#conditionally-importing-and-exporting-library-files" aria-label="Link to 'Conditionally importing and exporting library files' section">#</a></div><p>If your library supports multiple platforms, then you might need to conditionally import or export library files. A common use case is a library that supports both web and native platforms.</p><p>To conditionally import or export, you need to check for the presence of <code>dart:*</code> libraries. Here's an example of conditional export code that checks for the presence of <code>dart:io</code> and <code>dart:js_interop</code>:</p> <?code-excerpt "create_libraries/lib/hw_mp.dart (export)"?> <div class="code-block-wrapper language-dart"><div class="code-block-header">lib/hw_mp.dart</div><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">export</span><span style="color:#11796D"> 'src/hw_none.dart'</span><span style="color:#6E6E70"> // Stub implementation</span></span> <span class="line"><span style="color:#D43324"> if</span><span style="color:#222222"> (dart.library.io) </span><span style="color:#11796D">'src/hw_io.dart'</span><span style="color:#6E6E70"> // dart:io implementation</span></span> <span class="line"><span style="color:#D43324"> if</span><span style="color:#222222"> (dart.library.js_interop) </span><span style="color:#11796D">'src/hw_web.dart'</span><span style="color:#222222">; </span><span style="color:#6E6E70">// package:web implementation</span></span></code></pre></div></div><p>Here's what that code does:</p><ul><li>In an app that can use <code>dart:io</code> (for example, a command-line app), export <code>src/hw_io.dart</code>.</li><li>In an app that can use <code>dart:js_interop</code> (a web app), export <code>src/hw_web.dart</code>.</li><li>Otherwise, export <code>src/hw_none.dart</code>.</li></ul><p>To conditionally import a file, use the same code as above, but change <code>export</code> to <code>import</code>.</p><aside class="alert alert-info"><div class="alert-header"><span class="material-symbols" aria-hidden="true">info</span> <span>Note</span></div><div class="alert-content"><p>Conditional imports or exports only work with keys in the compilation environment. Any sequence of dot-separated identifiers is valid syntax. Currently, only keys of the form <code>dart.library.name</code> are provided. <code>dart.library.name</code> is set to <code>"true"</code> in the compilation environment if the library <code>dart:name</code> is <em>available for use</em> on the current platform, not whether it's actually imported or used.</p></div></aside><p>All of the conditionally exported libraries must implement the same API. For example, here's the <code>dart:io</code> implementation:</p> <?code-excerpt "create_libraries/lib/src/hw_io.dart"?> <div class="code-block-wrapper language-dart"><div class="code-block-header">lib/src/hw_io.dart</div><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">import</span><span style="color:#11796D"> 'dart:io'</span><span style="color:#222222">;</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">void</span><span style="color:#6200EE"> alarm</span><span style="color:#222222">([</span><span style="color:#0468D7">String</span><span style="color:#222222">? text]) {</span></span> <span class="line"><span style="color:#222222"> stderr.</span><span style="color:#6200EE">writeln</span><span style="color:#222222">(text ?? message);</span></span> <span class="line"><span style="color:#222222">}</span></span> <span class="line"></span> <span class="line"><span style="color:#0468D7">String</span><span style="color:#D43324"> get</span><span style="color:#222222"> message => </span><span style="color:#11796D">'Hello World from the VM!'</span><span style="color:#222222">;</span></span></code></pre></div></div><p>And here's the default implementation, which uses stubs that throw <code>UnsupportedError</code>:</p> <?code-excerpt "create_libraries/lib/src/hw_none.dart"?> <div class="code-block-wrapper language-dart"><div class="code-block-header">lib/src/hw_none.dart</div><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">void</span><span style="color:#6200EE"> alarm</span><span style="color:#222222">([</span><span style="color:#0468D7">String</span><span style="color:#222222">? text]) => </span><span style="color:#D43324">throw</span><span style="color:#0468D7"> UnsupportedError</span><span style="color:#222222">(</span><span style="color:#11796D">'hw_none alarm'</span><span style="color:#222222">);</span></span> <span class="line"></span> <span class="line"><span style="color:#0468D7">String</span><span style="color:#D43324"> get</span><span style="color:#222222"> message => </span><span style="color:#D43324">throw</span><span style="color:#0468D7"> UnsupportedError</span><span style="color:#222222">(</span><span style="color:#11796D">'hw_none message'</span><span style="color:#222222">);</span></span></code></pre></div></div><p>On any platform, you can import the library that has the conditional export code:</p> <?code-excerpt "create_libraries/example/hw_example.dart" replace="/create_libraries/hw_mp/g"?> <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">import</span><span style="color:#11796D"> 'package:hw_mp/hw_mp.dart'</span><span style="color:#222222">;</span></span> <span class="line"></span> <span class="line"><span style="color:#D43324">void</span><span style="color:#6200EE"> main</span><span style="color:#222222">() {</span></span> <span class="line"><span style="color:#6200EE"> print</span><span style="color:#222222">(message);</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><div class="header-wrapper"><h2 id="providing-additional-files">Providing additional files</h2><a class="heading-link" href="#providing-additional-files" aria-label="Link to 'Providing additional files' section">#</a></div><p>A well-designed package is easy to test. We recommend that you write tests using the <a href="https://github.com/dart-lang/test">test</a> package, placing the test code in the <code>test</code> directory at the top of the package.</p><p>If you create any command-line tools intended for public consumption, place those in the <code>bin</code> directory, which is public. Enable running a tool from the command line, using <a href="/tools/pub/cmd/pub-global#activating-a-package"><code>dart pub global activate</code></a>. Listing the tool in the <a href="/tools/pub/pubspec#executables"><code>executables</code> section</a> of the pubspec allows a user to run it directly without calling <a href="/tools/pub/cmd/pub-global#running-a-script-using-dart-pub-global-run"><code>dart pub global run</code></a>.</p><p>It's helpful if you include an example of how to use your library. This goes into the <code>example</code> directory at the top of the package.</p><p>Any tools or executables that you create during development that aren't for public use go into the <code>tool</code> directory.</p><p>Other files that are required if you publish your library to the <a href="https://pub.dev">pub.dev</a> site, such as <code>README.md</code> and <code>CHANGELOG.md</code>, are described in <a href="/tools/pub/publishing">Publishing a package</a>. For more information on how to organize a package directory, see the <a href="/tools/pub/package-layout">pub package layout conventions</a>.</p><div class="header-wrapper"><h2 id="documenting-a-library">Documenting a library</h2><a class="heading-link" href="#documenting-a-library" aria-label="Link to 'Documenting a library' section">#</a></div><p>You can generate API docs for your library using the <a href="/tools/dart-doc"><code>dart doc</code></a> tool. <code>dart doc</code> parses the source looking for <a href="/effective-dart/documentation#doc-comments">documentation comments</a>, which use the <code>///</code> syntax:</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:#6E6E70">/// The event handler responsible for updating the badge in the UI.</span></span> <span class="line"><span style="color:#D43324">void</span><span style="color:#6200EE"> updateBadge</span><span style="color:#222222">() {</span></span> <span class="line"><span style="color:#222222"> ...</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><p>For an example of generated docs, see the <a href="https://pub.dev/documentation/shelf/latest">shelf documentation.</a></p><p>To include any <em>library-level</em> documentation in the generated docs, add a <code>library</code> directive and attach the comment directly above it. For the how-and-why of documenting libraries, see <a href="/effective-dart/documentation#consider-writing-a-library-level-doc-comment">Effective Dart: Documentation</a>.</p><div class="header-wrapper"><h2 id="distributing-a-library">Distributing an open source library</h2><a class="heading-link" href="#distributing-a-library" aria-label="Link to 'Distributing an open source library' section">#</a></div><p>If your library is open source, we recommend sharing it on the <a href="https://pub.dev">pub.dev site.</a> To publish or update the library, use <a href="/tools/pub/cmd/pub-lish">pub publish</a>, which uploads your package and creates or updates its page. For example, see the page for the <a href="https://pub.dev/packages/shelf">shelf package.</a> See <a href="/tools/pub/publishing">Publishing a package</a> for details on how to prepare your package for publishing.</p><p>The pub.dev site not only hosts your package, but also generates and hosts your package's API reference docs. A link to the latest generated docs is in the package's <strong>About</strong> box; for example, see the shelf package's <a href="https://pub.dev/documentation/shelf">API docs.</a> Links to previous versions' docs are in the <strong>Versions</strong> tab of the package's page.</p><p>To ensure that your package's API docs look good on the pub.dev site, follow these steps:</p><ul><li>Before publishing your package, run the <a href="/tools/dart-doc"><code>dart doc</code></a> tool to make sure that your docs generate successfully and look as expected.</li><li>After publishing your package, check the <strong>Versions</strong> tab to make sure that the docs generated successfully.</li><li>If the docs didn't generate at all, click <strong>failed</strong> in the <strong>Versions</strong> tab to see the <code>dart doc</code> output.</li></ul><div class="header-wrapper"><h2 id="resources">Resources</h2><a class="heading-link" href="#resources" aria-label="Link to 'Resources' section">#</a></div><p>Use the following resources to learn more about packages:</p><ul><li><a href="/language/libraries">Libraries and imports</a> covers using library files.</li><li>The <a href="/tools/pub/packages">package</a> documentation is useful, particularly the <a href="/tools/pub/package-layout">package layout conventions</a>.</li><li><a href="/tools/pub/private-files">What not to commit</a> covers what shouldn't be checked into a source code repository.</li><li>The newer packages under the <a href="https://github.com/dart-lang">dart-lang</a> organization tend to show best practices. Consider studying these examples: <a href="https://github.com/dart-lang/dart_style">dart_style,</a> <a href="https://github.com/dart-lang/path">path,</a> <a href="https://github.com/dart-lang/shelf">shelf,</a> <a href="https://github.com/dart-lang/source_gen">source_gen,</a> and <a href="https://github.com/dart-lang/test">test.</a></li></ul><p id="page-github-links"><span>Unless stated otherwise, the documentation on this site reflects Dart 3.7.0. Page last updated on 2024-12-10.</span> <a href="https://github.com/dart-lang/site-www/tree/main/src/content/tools/pub/create-packages.md" target="_blank" rel="noopener">View source</a> <span>or </span><a href="https://github.com/dart-lang/site-www/issues/new?template=1_page_issue.yml&page-url=https://dart.dev/tools/pub/create-packages/&page-source=https://github.com/dart-lang/site-www/tree/main/src/content/tools/pub/create-packages.md" title="Report an issue with this page" target="_blank" rel="noopener">report an issue</a>.</p></div></article></main></div><footer id="page-footer"><div class="footer-section footer-main"><a href="/" class="brand" title="Dart"><img src="/assets/img/logo/logo-white-text.svg" alt="Dart" width="164"></a><div class="footer-social-links"><a href="https://medium.com/dartlang" target="_blank" rel="noopener" title="Dart's Medium publication"><svg><use href="/assets/img/social/medium.svg#medium"></use></svg> </a><a href="https://github.com/dart-lang" target="_blank" rel="noopener" title="Dart's GitHub organization"><svg><use href="/assets/img/social/github.svg#github"></use></svg> </a><a href="https://bsky.app/profile/dart.dev" target="_blank" rel="noopener" title="Dart's Bluesky profile"><svg><use href="/assets/img/social/bluesky.svg#bluesky"></use></svg> </a><a href="https://twitter.com/dart_lang" target="_blank" rel="noopener" title="Dart's X (Twitter) profile"><svg><use href="/assets/img/social/x.svg#x"></use></svg></a></div></div><div class="footer-section footer-tray"><div class="footer-licenses">Except as otherwise noted, this site is licensed under a <a href="https://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>, and code samples are licensed under the <a href="https://opensource.org/licenses/BSD-3-Clause">3-Clause BSD License</a>.</div><div class="footer-utility-links"><ul><li><a href="/terms" title="Terms of use">Terms</a></li><li><a href="https://policies.google.com/privacy" target="_blank" rel="noopener" title="Privacy policy">Privacy</a></li><li><a href="/security" title="Security philosophy and practices">Security</a></li></ul></div></div></footer></div></body></html>