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<ul class="chapter"><li><a href="ch01-00-introduction.html"><strong>1.</strong> Introduction</a></li><li><ul class="section"><li><a href="ch01-01-installation.html"><strong>1.1.</strong> Installation</a></li><li><a href="ch01-02-hello-world.html"><strong>1.2.</strong> Hello, World!</a></li></ul></li><li><a href="ch02-00-guessing-game-tutorial.html"><strong>2.</strong> Guessing Game Tutorial</a></li><li><a href="ch03-00-common-programming-concepts.html"><strong>3.</strong> Common Programming Concepts</a></li><li><ul class="section"><li><a href="ch03-01-variables-and-mutability.html"><strong>3.1.</strong> Variables and Mutability</a></li><li><a href="ch03-02-data-types.html"><strong>3.2.</strong> Data Types</a></li><li><a href="ch03-03-how-functions-work.html"><strong>3.3.</strong> How Functions Work</a></li><li><a href="ch03-04-comments.html"><strong>3.4.</strong> Comments</a></li><li><a href="ch03-05-control-flow.html"><strong>3.5.</strong> Control Flow</a></li></ul></li><li><a href="ch04-00-understanding-ownership.html"><strong>4.</strong> Understanding Ownership</a></li><li><ul class="section"><li><a href="ch04-01-what-is-ownership.html"><strong>4.1.</strong> What is Ownership?</a></li><li><a href="ch04-02-references-and-borrowing.html"><strong>4.2.</strong> References & Borrowing</a></li><li><a href="ch04-03-slices.html"><strong>4.3.</strong> Slices</a></li></ul></li><li><a href="ch05-00-structs.html"><strong>5.</strong> Using Structs to Structure Related Data</a></li><li><ul class="section"><li><a href="ch05-01-defining-structs.html"><strong>5.1.</strong> Defining and Instantiating Structs</a></li><li><a href="ch05-02-example-structs.html"><strong>5.2.</strong> An Example Program Using Structs</a></li><li><a href="ch05-03-method-syntax.html"><strong>5.3.</strong> Method Syntax</a></li></ul></li><li><a href="ch06-00-enums.html"><strong>6.</strong> Enums and Pattern Matching</a></li><li><ul class="section"><li><a href="ch06-01-defining-an-enum.html"><strong>6.1.</strong> Defining an Enum</a></li><li><a href="ch06-02-match.html"><strong>6.2.</strong> The <code>match</code> Control Flow Operator</a></li><li><a href="ch06-03-if-let.html"><strong>6.3.</strong> Concise Control Flow with <code>if let</code></a></li></ul></li><li><a href="ch07-00-modules.html" class="active"><strong>7.</strong> Modules</a></li><li><ul class="section"><li><a href="ch07-01-mod-and-the-filesystem.html"><strong>7.1.</strong> <code>mod</code> and the Filesystem</a></li><li><a href="ch07-02-controlling-visibility-with-pub.html"><strong>7.2.</strong> Controlling Visibility with <code>pub</code></a></li><li><a href="ch07-03-importing-names-with-use.html"><strong>7.3.</strong> Importing Names with <code>use</code></a></li></ul></li><li><a href="ch08-00-common-collections.html"><strong>8.</strong> Common Collections</a></li><li><ul class="section"><li><a href="ch08-01-vectors.html"><strong>8.1.</strong> Vectors</a></li><li><a href="ch08-02-strings.html"><strong>8.2.</strong> Strings</a></li><li><a href="ch08-03-hash-maps.html"><strong>8.3.</strong> Hash Maps</a></li></ul></li><li><a href="ch09-00-error-handling.html"><strong>9.</strong> Error Handling</a></li><li><ul class="section"><li><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong>9.1.</strong> Unrecoverable Errors with <code>panic!</code></a></li><li><a href="ch09-02-recoverable-errors-with-result.html"><strong>9.2.</strong> Recoverable Errors with <code>Result</code></a></li><li><a href="ch09-03-to-panic-or-not-to-panic.html"><strong>9.3.</strong> To <code>panic!</code> or Not To <code>panic!</code></a></li></ul></li><li><a href="ch10-00-generics.html"><strong>10.</strong> Generic Types, Traits, and Lifetimes</a></li><li><ul class="section"><li><a href="ch10-01-syntax.html"><strong>10.1.</strong> Generic Data Types</a></li><li><a href="ch10-02-traits.html"><strong>10.2.</strong> Traits: Defining Shared Behavior</a></li><li><a href="ch10-03-lifetime-syntax.html"><strong>10.3.</strong> Validating References with Lifetimes</a></li></ul></li><li><a href="ch11-00-testing.html"><strong>11.</strong> Testing</a></li><li><ul class="section"><li><a href="ch11-01-writing-tests.html"><strong>11.1.</strong> Writing tests</a></li><li><a href="ch11-02-running-tests.html"><strong>11.2.</strong> Running tests</a></li><li><a href="ch11-03-test-organization.html"><strong>11.3.</strong> Test Organization</a></li></ul></li><li><a href="ch12-00-an-io-project.html"><strong>12.</strong> An I/O Project</a></li><li><ul class="section"><li><a href="ch12-01-accepting-command-line-arguments.html"><strong>12.1.</strong> Accepting Command Line Arguments</a></li><li><a href="ch12-02-reading-a-file.html"><strong>12.2.</strong> Reading a File</a></li><li><a href="ch12-03-improving-error-handling-and-modularity.html"><strong>12.3.</strong> Improving Error Handling and Modularity</a></li><li><a href="ch12-04-testing-the-librarys-functionality.html"><strong>12.4.</strong> Testing the Library's Functionality</a></li><li><a href="ch12-05-working-with-environment-variables.html"><strong>12.5.</strong> Working with Environment Variables</a></li><li><a href="ch12-06-writing-to-stderr-instead-of-stdout.html"><strong>12.6.</strong> Writing to <code>stderr</code> instead of <code>stdout</code></a></li></ul></li><li><a href="ch13-00-functional-features.html"><strong>13.</strong> Functional Language Features in Rust</a></li><li><ul class="section"><li><a href="ch13-01-closures.html"><strong>13.1.</strong> Closures</a></li><li><a href="ch13-02-iterators.html"><strong>13.2.</strong> Iterators</a></li><li><a href="ch13-03-improving-our-io-project.html"><strong>13.3.</strong> Improving our I/O Project</a></li><li><a href="ch13-04-performance.html"><strong>13.4.</strong> Performance</a></li></ul></li><li><a href="ch14-00-more-about-cargo.html"><strong>14.</strong> More about Cargo and Crates.io</a></li><li><ul class="section"><li><a href="ch14-01-release-profiles.html"><strong>14.1.</strong> Release Profiles</a></li><li><a href="ch14-02-publishing-to-crates-io.html"><strong>14.2.</strong> Publishing a Crate to Crates.io</a></li><li><a href="ch14-03-cargo-workspaces.html"><strong>14.3.</strong> Cargo Workspaces</a></li><li><a href="ch14-04-installing-binaries.html"><strong>14.4.</strong> Installing Binaries from Crates.io with <code>cargo install</code></a></li><li><a href="ch14-05-extending-cargo.html"><strong>14.5.</strong> Extending Cargo with Custom Commands</a></li></ul></li><li><a href="ch15-00-smart-pointers.html"><strong>15.</strong> Smart Pointers</a></li><li><ul class="section"><li><a href="ch15-01-box.html"><strong>15.1.</strong> <code>Box<T></code> Points to Data on the Heap and Has a Known Size</a></li><li><a href="ch15-02-deref.html"><strong>15.2.</strong> The <code>Deref</code> Trait Allows Access to the Data Through a Reference</a></li><li><a href="ch15-03-drop.html"><strong>15.3.</strong> The <code>Drop</code> Trait Runs Code on Cleanup</a></li><li><a href="ch15-04-rc.html"><strong>15.4.</strong> <code>Rc<T></code>, the Reference Counted Smart Pointer</a></li><li><a href="ch15-05-interior-mutability.html"><strong>15.5.</strong> <code>RefCell<T></code> and the Interior Mutability Pattern</a></li><li><a href="ch15-06-reference-cycles.html"><strong>15.6.</strong> Creating Reference Cycles and Leaking Memory is Safe</a></li></ul></li><li><a href="ch16-00-concurrency.html"><strong>16.</strong> Fearless Concurrency</a></li><li><ul class="section"><li><a href="ch16-01-threads.html"><strong>16.1.</strong> Threads</a></li><li><a href="ch16-02-message-passing.html"><strong>16.2.</strong> Message Passing</a></li><li><a href="ch16-03-shared-state.html"><strong>16.3.</strong> Shared State</a></li><li><a href="ch16-04-extensible-concurrency-sync-and-send.html"><strong>16.4.</strong> Extensible Concurrency: <code>Sync</code> and <code>Send</code></a></li></ul></li><li><a href="ch17-00-oop.html"><strong>17.</strong> Is Rust an Object-Oriented Programming Language?</a></li><li><ul class="section"><li><a href="ch17-01-what-is-oo.html"><strong>17.1.</strong> What Does Object-Oriented Mean?</a></li><li><a href="ch17-02-trait-objects.html"><strong>17.2.</strong> Trait Objects for Using Values of Different Types</a></li><li><a href="ch17-03-oo-design-patterns.html"><strong>17.3.</strong> Object-Oriented Design Pattern Implementations</a></li></ul></li><li><a href="ch18-00-patterns.html"><strong>18.</strong> Patterns Match the Structure of Values</a></li><li><ul class="section"><li><a href="ch18-01-all-the-places-for-patterns.html"><strong>18.1.</strong> All the Places Patterns May be Used</a></li><li><a href="ch18-02-refutability.html"><strong>18.2.</strong> Refutability: Whether a Pattern Might Fail to Match</a></li><li><a href="ch18-03-pattern-syntax.html"><strong>18.3.</strong> All the Pattern Syntax</a></li></ul></li><li><a href="ch19-00-advanced-features.html"><strong>19.</strong> Advanced Features</a></li><li><ul class="section"><li><a href="ch19-01-unsafe-rust.html"><strong>19.1.</strong> Unsafe Rust</a></li><li><a href="ch19-02-advanced-lifetimes.html"><strong>19.2.</strong> Advanced Lifetimes</a></li><li><a href="ch19-03-advanced-traits.html"><strong>19.3.</strong> Advanced Traits</a></li><li><a href="ch19-04-advanced-types.html"><strong>19.4.</strong> Advanced Types</a></li><li><a href="ch19-05-advanced-functions-and-closures.html"><strong>19.5.</strong> Advanced Functions & Closures</a></li></ul></li><li><a href="ch20-00-final-project-a-web-server.html"><strong>20.</strong> Final Project: Building a Multithreaded Web Server</a></li><li><ul class="section"><li><a href="ch20-01-single-threaded.html"><strong>20.1.</strong> A Single Threaded Web Server</a></li><li><a href="ch20-02-slow-requests.html"><strong>20.2.</strong> How Slow Requests Affect Throughput</a></li><li><a href="ch20-03-designing-the-interface.html"><strong>20.3.</strong> Designing the Thread Pool Interface</a></li><li><a href="ch20-04-storing-threads.html"><strong>20.4.</strong> Creating the Thread Pool and Storing Threads</a></li><li><a href="ch20-05-sending-requests-via-channels.html"><strong>20.5.</strong> Sending Requests to Threads Via Channels</a></li><li><a href="ch20-06-graceful-shutdown-and-cleanup.html"><strong>20.6.</strong> Graceful Shutdown and Cleanup</a></li></ul></li><li><a href="appendix-00.html"><strong>21.</strong> Appendix</a></li><li><ul class="section"><li><a href="appendix-01-keywords.html"><strong>21.1.</strong> A - Keywords</a></li><li><a href="appendix-02-operators.html"><strong>21.2.</strong> B - Operators</a></li><li><strong>21.3.</strong> C - Derivable Traits</li><li><strong>21.4.</strong> D - Nightly Rust</li><li><strong>21.5.</strong> E - Macros</li><li><strong>21.6.</strong> F - Translations</li><li><a href="appendix-07-newest-features.html"><strong>21.7.</strong> G - Newest Features</a></li></ul></li></ul>
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<h1 class="menu-title">The Rust Programming Language</h1>
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<a class="header" href="ch07-00-modules.html#using-modules-to-reuse-and-organize-code" id="using-modules-to-reuse-and-organize-code"><h1>Using Modules to Reuse and Organize Code</h1></a>
<p>When you start writing programs in Rust, your code might live solely in the
<code>main</code> function. As your code grows, you’ll eventually move functionality into
other functions for reuse and better organization. By splitting your code into
smaller chunks, each chunk is easier to understand on its own. But what happens
if you have too many functions? Rust has a module system that enables the reuse
of code in an organized fashion.</p>
<p>In the same way that you extract lines of code into a function, you can extract
functions (and other code, like structs and enums) into different modules. A
<em>module</em> is a namespace that contains definitions of functions or types, and
you can choose whether those definitions are visible outside their module
(public) or not (private). Here’s an overview of how modules work:</p>
<ul>
<li>The <code>mod</code> keyword declares a new module. Code within the module appears
either immediately following this declaration within curly braces or in
another file.</li>
<li>By default, functions, types, constants, and modules are private. The <code>pub</code>
keyword makes an item public and therefore visible outside its namespace.</li>
<li>The <code>use</code> keyword brings modules, or the definitions inside modules, into
scope so it’s easier to refer to them.</li>
</ul>
<p>We’ll look at each of these parts to see how they fit into the whole.</p>
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