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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 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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="#accessing-environment-declarations">Accessing environment declarations</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#specifying-environment-declarations">Specifying environment declarations</a><ul class="nav"><li class="toc-entry nav-item"><a class="nav-link" href="#dart-cli">Dart CLI</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#visual-studio-code">Visual Studio Code</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#jetbrains-ides">JetBrains IDEs</a></li><li class="toc-entry nav-item"><a class="nav-link" href="#flutter">Flutter</a></li></ul></li></ul></div><article><div class="content"><div id="site-content-title"><h1>Configuring apps with compilation environment declarations</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="#accessing-environment-declarations">Accessing environment declarations</a></li><li class="toc-entry"><a href="#specifying-environment-declarations">Specifying environment declarations</a><ul><li class="toc-entry"><a href="#dart-cli">Dart CLI</a></li><li class="toc-entry"><a href="#visual-studio-code">Visual Studio Code</a></li><li class="toc-entry"><a href="#jetbrains-ides">JetBrains IDEs</a></li><li class="toc-entry"><a href="#flutter">Flutter</a></li></ul></li></ul></div><p>You can specify compilation environment declarations when building or running a Dart application. Compilation environment declarations specify configuration options as key-value pairs that are accessed and evaluated at compile time.</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>This page uses "environment" to refer to the Dart compilation environment. The common use of the term instead refers to the operating system environment.</p></div></aside><p>Your app can use the values of environment declarations to change its functionality or behavior. Dart compilers can eliminate the code made unreachable due to control flow using the environment declaration values.</p><p>You might define and use environment declarations to:</p><ul><li>Add functionality during debugging, such as enabling logging.</li><li>Create separate flavors of your application.</li><li>Configure application behavior, such as the port of an HTTP server.</li><li>Enable an experimental mode of your application for testing.</li><li>Switch between testing and production backends.</li></ul><p>To specify an environment declaration when running or compiling a Dart application, use the <code>--define</code> option or its abbreviation, <code>-D</code>. Specify the declaration key-value pair using a <code><NAME>=<VALUE></code> format:</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 run --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span></span></code></pre></div></div><p>To learn how to set these declarations with other tools, check out the <a href="#specifying-environment-declarations">specifying environment declarations</a> section in this guide. That section explains the declaration syntax and how to specify them on the command line and in IDEs and editors.</p><div class="header-wrapper"><h2 id="accessing-environment-declarations">Accessing environment declarations</h2><a class="heading-link" href="#accessing-environment-declarations" aria-label="Link to 'Accessing environment declarations' section">#</a></div><p>To access specified environment declaration values, use one of the <code>fromEnvironment</code> constructors with <code>const</code> or within a constant context. Use <a href="https://api.dart.dev/dart-core/bool/bool.fromEnvironment.html"><code>bool.fromEnvironment</code></a> for <code>true</code> or <code>false</code> values, <a href="https://api.dart.dev/dart-core/int/int.fromEnvironment.html"><code>int.fromEnvironment</code></a> for integer values, and <a href="https://api.dart.dev/dart-core/String/String.fromEnvironment.html"><code>String.fromEnvironment</code></a> for anything else.</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>The environment declaration constructors are only guaranteed to work when invoked as <code>const</code>. Most compilers must be able to evaluate their value at compile time.</p></div></aside><p>Each of the <code>fromEnvironment</code> constructors require the name or key of the environment declaration. They also accept an optional <code>defaultValue</code> named argument to override the default fallback value. The default fallback value is used when a declaration isn't defined or the specified value cannot be parsed as the expected type.</p><p>For example, if you want to print log messages only when the environment declaration <code>DEBUG</code> is set to <code>true</code>:</p> <?code-excerpt "misc/lib/development/environment_declarations.dart (debug-log)"?> <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">void</span><span style="color:#6200EE"> log</span><span style="color:#222222">(</span><span style="color:#0468D7">String</span><span style="color:#222222"> message) {</span></span> <span class="line"><span style="color:#6E6E70"> // Log the debug message if the environment declaration 'DEBUG' is `true`.</span></span> <span class="line"><span style="color:#6E6E70"> // If there was no value specified, do not log.</span></span> <span class="line"><span style="color:#D43324"> if</span><span style="color:#222222"> (</span><span style="color:#D43324">const</span><span style="color:#0468D7"> bool</span><span style="color:#222222">.</span><span style="color:#6200EE">fromEnvironment</span><span style="color:#222222">(</span><span style="color:#11796D">'DEBUG'</span><span style="color:#222222">, defaultValue: </span><span style="color:#11796D">false</span><span style="color:#222222">)) {</span></span> <span class="line"><span style="color:#6200EE"> print</span><span style="color:#222222">(</span><span style="color:#11796D">'Debug: </span><span style="color:#11796D">$</span><span style="color:#222222">message</span><span style="color:#11796D">'</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>In this snippet, if <code>DEBUG</code> is set to <code>false</code> during compilation, or not specified at all, production compilers can completely remove the condition and its body.</p><p>The <code>fromEnvironment</code> constructors fallback to a default value when the declaration isn't specified or the specified value cannot be parsed. Therefore, to specifically check whether an environment declaration has been specified, use the <a href="https://api.dart.dev/dart-core/bool/bool.hasEnvironment.html"><code>bool.hasEnvironment</code></a> constructor:</p> <?code-excerpt "misc/lib/development/environment_declarations.dart (has-debug)"?> <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">if</span><span style="color:#222222"> (</span><span style="color:#D43324">const</span><span style="color:#0468D7"> bool</span><span style="color:#222222">.</span><span style="color:#6200EE">hasEnvironment</span><span style="color:#222222">(</span><span style="color:#11796D">'DEBUG'</span><span style="color:#222222">)) {</span></span> <span class="line"><span style="color:#6200EE"> print</span><span style="color:#222222">(</span><span style="color:#11796D">'Debug behavior was configured!'</span><span style="color:#222222">);</span></span> <span class="line"><span style="color:#222222">}</span></span></code></pre></div></div><div class="header-wrapper"><h2 id="specifying-environment-declarations">Specifying environment declarations</h2><a class="heading-link" href="#specifying-environment-declarations" aria-label="Link to 'Specifying environment declarations' section">#</a></div><aside class="alert alert-warning"><div class="alert-header"><span class="material-symbols" aria-hidden="true">warning</span> <span>Warning</span></div><div class="alert-content"><p>Dart tools and compilers currently do not consistently handle environment declarations with comma-separated values. To track standardization of this handling, reference <a href="https://github.com/dart-lang/sdk/issues/44995">SDK issue 44995</a>.</p></div></aside><div class="header-wrapper"><h3 id="dart-cli">Dart CLI</h3><a class="heading-link" href="#dart-cli" aria-label="Link to 'Dart CLI' section">#</a></div><p>Both <code>dart run</code> and the <code>dart compile</code> subcommands accept any number of the <code>-D</code> or <code>--define</code> options to specify environment declaration values.</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 run --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span><span style="color:#6200EE"> main.dart</span></span> <span class="line"><span style="color:#222222">$ dart compile exe --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span><span style="color:#6200EE"> main.dart</span></span> <span class="line"><span style="color:#222222">$ dart compile js --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span><span style="color:#6200EE"> main.dart</span></span> <span class="line"><span style="color:#222222">$ dart compile aot-snapshot --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span><span style="color:#6200EE"> main.dart</span></span> <span class="line"><span style="color:#222222">$ dart compile jit-snapshot --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span><span style="color:#6200EE"> main.dart</span></span> <span class="line"><span style="color:#222222">$ dart compile kernel --define=DEBUG=</span><span style="color:#11796D">true</span><span style="color:#222222"> -DFLAVOR=</span><span style="color:#11796D">free</span><span style="color:#6200EE"> main.dart</span></span></code></pre></div></div><div class="header-wrapper"><h4 id="webdev"><code>webdev</code></h4><a class="heading-link" href="#webdev" aria-label="Link to 'webdev' section">#</a></div><p>To learn about configuring <code>webdev</code> to pass environment declarations to both the development and production web compilers, check out <a href="https://pub.dev/packages/build_web_compilers#configuring--d-environment-variables">the <code>webdev</code> configuration documentation</a>.</p><div class="header-wrapper"><h3 id="visual-studio-code">Visual Studio Code</h3><a class="heading-link" href="#visual-studio-code" aria-label="Link to 'Visual Studio Code' section">#</a></div><p>In your launch configuration (<code>launch.json</code>) under <code>configurations</code>, add a new <code>toolArgs</code> key containing your desired environment declarations:</p><div class="code-block-wrapper language-json"><div class="code-block-body"><span class="code-block-language" title="Language json">json</span><pre class="shiki dash-light" tabindex="0"><code><span class="line"><span style="color:#11796D">"configurations"</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 style="color:#0468D7">name</span><span style="color:#222222">"</span><span style="color:#222222">: </span><span style="color:#11796D">"Dart"</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222"> "</span><span style="color:#0468D7">request</span><span style="color:#222222">"</span><span style="color:#222222">: </span><span style="color:#11796D">"launch"</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222"> "</span><span style="color:#0468D7">type</span><span style="color:#222222">"</span><span style="color:#222222">: </span><span style="color:#11796D">"dart"</span><span style="color:#222222">,</span></span> <span class="line"><span style="color:#222222"> "</span><span style="color:#0468D7">toolArgs</span><span style="color:#222222">"</span><span style="color:#222222">: [</span></span> <span class="line"><span style="color:#11796D"> "--define=DEBUG=true"</span></span> <span class="line"><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>To learn more, check out the documentation for <a href="https://code.visualstudio.com/docs/editor/debugging#_launch-configurations">VS Code launch configurations.</a></p><div class="header-wrapper"><h3 id="jetbrains-ides">JetBrains IDEs</h3><a class="heading-link" href="#jetbrains-ides" aria-label="Link to 'JetBrains IDEs' section">#</a></div><p>In the <strong>Run/Debug Configurations</strong> for your project, add your desired environment declarations to <strong>VM options</strong>:</p><p><img src="/assets/img/env-decl-jetbrains.png" alt="Adding define option to Jetbrains IDE"></p><p>To learn more, check out JetBrains' documentation for <a href="https://www.jetbrains.com/help/webstorm/run-debug-configuration-dart-command-line-application.html">Dart Run/Debug Configurations</a>.</p><div class="header-wrapper"><h3 id="flutter">Flutter</h3><a class="heading-link" href="#flutter" aria-label="Link to 'Flutter' section">#</a></div><p>To specify environment declarations to the Flutter tool, use the <code>--dart-define</code> option instead:</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">$ flutter run --dart-define=DEBUG=</span><span style="color:#11796D">true</span></span></code></pre></div></div><p id="page-github-links"><span>Unless stated otherwise, the documentation on this site reflects Dart 3.7.0. 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