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<ol class="chapter"><li class="expanded affix "><a href="title-page.html">The Rust Programming Language</a></li><li class="expanded affix "><a href="foreword.html">Foreword</a></li><li class="expanded affix "><a href="ch00-00-introduction.html">Introduction</a></li><li class="expanded "><a href="ch01-00-getting-started.html"><strong aria-hidden="true">1.</strong> Getting Started</a></li><li><ol class="section"><li class="expanded "><a href="ch01-01-installation.html"><strong aria-hidden="true">1.1.</strong> Installation</a></li><li class="expanded "><a href="ch01-02-hello-world.html"><strong aria-hidden="true">1.2.</strong> Hello, World!</a></li><li class="expanded "><a href="ch01-03-hello-cargo.html"><strong aria-hidden="true">1.3.</strong> Hello, Cargo!</a></li></ol></li><li class="expanded "><a href="ch02-00-guessing-game-tutorial.html"><strong aria-hidden="true">2.</strong> Programming a Guessing Game</a></li><li class="expanded "><a href="ch03-00-common-programming-concepts.html"><strong aria-hidden="true">3.</strong> Common Programming Concepts</a></li><li><ol class="section"><li class="expanded "><a href="ch03-01-variables-and-mutability.html"><strong aria-hidden="true">3.1.</strong> Variables and Mutability</a></li><li class="expanded "><a href="ch03-02-data-types.html"><strong aria-hidden="true">3.2.</strong> Data Types</a></li><li class="expanded "><a href="ch03-03-how-functions-work.html"><strong aria-hidden="true">3.3.</strong> Functions</a></li><li class="expanded "><a href="ch03-04-comments.html"><strong aria-hidden="true">3.4.</strong> Comments</a></li><li class="expanded "><a href="ch03-05-control-flow.html"><strong aria-hidden="true">3.5.</strong> Control Flow</a></li></ol></li><li class="expanded "><a href="ch04-00-understanding-ownership.html"><strong aria-hidden="true">4.</strong> Understanding Ownership</a></li><li><ol class="section"><li class="expanded "><a href="ch04-01-what-is-ownership.html"><strong aria-hidden="true">4.1.</strong> What is Ownership?</a></li><li class="expanded "><a href="ch04-02-references-and-borrowing.html"><strong aria-hidden="true">4.2.</strong> References and Borrowing</a></li><li class="expanded "><a href="ch04-03-slices.html"><strong aria-hidden="true">4.3.</strong> The Slice Type</a></li></ol></li><li class="expanded "><a href="ch05-00-structs.html"><strong aria-hidden="true">5.</strong> Using Structs to Structure Related Data</a></li><li><ol class="section"><li class="expanded "><a href="ch05-01-defining-structs.html"><strong aria-hidden="true">5.1.</strong> Defining and Instantiating Structs</a></li><li class="expanded "><a href="ch05-02-example-structs.html"><strong aria-hidden="true">5.2.</strong> An Example Program Using Structs</a></li><li class="expanded "><a href="ch05-03-method-syntax.html"><strong aria-hidden="true">5.3.</strong> Method Syntax</a></li></ol></li><li class="expanded "><a href="ch06-00-enums.html"><strong aria-hidden="true">6.</strong> Enums and Pattern Matching</a></li><li><ol class="section"><li class="expanded "><a href="ch06-01-defining-an-enum.html"><strong aria-hidden="true">6.1.</strong> Defining an Enum</a></li><li class="expanded "><a href="ch06-02-match.html"><strong aria-hidden="true">6.2.</strong> The match Control Flow Operator</a></li><li class="expanded "><a href="ch06-03-if-let.html"><strong aria-hidden="true">6.3.</strong> Concise Control Flow with if let</a></li></ol></li><li class="expanded "><a href="ch07-00-managing-growing-projects-with-packages-crates-and-modules.html"><strong aria-hidden="true">7.</strong> Managing Growing Projects with Packages, Crates, and Modules</a></li><li><ol class="section"><li class="expanded "><a href="ch07-01-packages-and-crates.html"><strong aria-hidden="true">7.1.</strong> Packages and Crates</a></li><li class="expanded "><a href="ch07-02-defining-modules-to-control-scope-and-privacy.html"><strong aria-hidden="true">7.2.</strong> Defining Modules to Control Scope and Privacy</a></li><li class="expanded "><a href="ch07-03-paths-for-referring-to-an-item-in-the-module-tree.html"><strong aria-hidden="true">7.3.</strong> Paths for Referring to an Item in the Module Tree</a></li><li class="expanded "><a href="ch07-04-bringing-paths-into-scope-with-the-use-keyword.html"><strong aria-hidden="true">7.4.</strong> Bringing Paths Into Scope with the use Keyword</a></li><li class="expanded "><a href="ch07-05-separating-modules-into-different-files.html"><strong aria-hidden="true">7.5.</strong> Separating Modules into Different Files</a></li></ol></li><li class="expanded "><a href="ch08-00-common-collections.html"><strong aria-hidden="true">8.</strong> Common Collections</a></li><li><ol class="section"><li class="expanded "><a href="ch08-01-vectors.html"><strong aria-hidden="true">8.1.</strong> Storing Lists of Values with Vectors</a></li><li class="expanded "><a href="ch08-02-strings.html"><strong aria-hidden="true">8.2.</strong> Storing UTF-8 Encoded Text with Strings</a></li><li class="expanded "><a href="ch08-03-hash-maps.html"><strong aria-hidden="true">8.3.</strong> Storing Keys with Associated Values in Hash Maps</a></li></ol></li><li class="expanded "><a href="ch09-00-error-handling.html"><strong aria-hidden="true">9.</strong> Error Handling</a></li><li><ol class="section"><li class="expanded "><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong aria-hidden="true">9.1.</strong> Unrecoverable Errors with panic!</a></li><li class="expanded "><a href="ch09-02-recoverable-errors-with-result.html"><strong aria-hidden="true">9.2.</strong> Recoverable Errors with Result</a></li><li class="expanded "><a href="ch09-03-to-panic-or-not-to-panic.html"><strong aria-hidden="true">9.3.</strong> To panic! or Not To panic!</a></li></ol></li><li class="expanded "><a href="ch10-00-generics.html"><strong aria-hidden="true">10.</strong> Generic Types, Traits, and Lifetimes</a></li><li><ol class="section"><li class="expanded "><a href="ch10-01-syntax.html"><strong aria-hidden="true">10.1.</strong> Generic Data Types</a></li><li class="expanded "><a href="ch10-02-traits.html"><strong aria-hidden="true">10.2.</strong> Traits: Defining Shared Behavior</a></li><li class="expanded "><a href="ch10-03-lifetime-syntax.html"><strong aria-hidden="true">10.3.</strong> Validating References with Lifetimes</a></li></ol></li><li class="expanded "><a href="ch11-00-testing.html"><strong aria-hidden="true">11.</strong> Writing Automated Tests</a></li><li><ol class="section"><li class="expanded "><a href="ch11-01-writing-tests.html"><strong aria-hidden="true">11.1.</strong> How to Write Tests</a></li><li class="expanded "><a href="ch11-02-running-tests.html"><strong aria-hidden="true">11.2.</strong> Controlling How Tests Are Run</a></li><li class="expanded "><a href="ch11-03-test-organization.html"><strong aria-hidden="true">11.3.</strong> Test Organization</a></li></ol></li><li class="expanded "><a href="ch12-00-an-io-project.html"><strong aria-hidden="true">12.</strong> An I/O Project: Building a Command Line Program</a></li><li><ol class="section"><li class="expanded "><a href="ch12-01-accepting-command-line-arguments.html"><strong aria-hidden="true">12.1.</strong> Accepting Command Line Arguments</a></li><li class="expanded "><a href="ch12-02-reading-a-file.html"><strong aria-hidden="true">12.2.</strong> Reading a File</a></li><li class="expanded "><a href="ch12-03-improving-error-handling-and-modularity.html"><strong aria-hidden="true">12.3.</strong> Refactoring to Improve Modularity and Error Handling</a></li><li class="expanded "><a href="ch12-04-testing-the-librarys-functionality.html"><strong aria-hidden="true">12.4.</strong> Developing the Library’s Functionality with Test Driven Development</a></li><li class="expanded "><a href="ch12-05-working-with-environment-variables.html"><strong aria-hidden="true">12.5.</strong> Working with Environment Variables</a></li><li class="expanded "><a href="ch12-06-writing-to-stderr-instead-of-stdout.html"><strong aria-hidden="true">12.6.</strong> Writing Error Messages to Standard Error Instead of Standard Output</a></li></ol></li><li class="expanded "><a href="ch13-00-functional-features.html"><strong aria-hidden="true">13.</strong> Functional Language Features: Iterators and Closures</a></li><li><ol class="section"><li class="expanded "><a href="ch13-01-closures.html"><strong aria-hidden="true">13.1.</strong> Closures: Anonymous Functions that Can Capture Their Environment</a></li><li class="expanded "><a href="ch13-02-iterators.html"><strong aria-hidden="true">13.2.</strong> Processing a Series of Items with Iterators</a></li><li class="expanded "><a href="ch13-03-improving-our-io-project.html"><strong aria-hidden="true">13.3.</strong> Improving Our I/O Project</a></li><li class="expanded "><a href="ch13-04-performance.html"><strong aria-hidden="true">13.4.</strong> Comparing Performance: Loops vs. Iterators</a></li></ol></li><li class="expanded "><a href="ch14-00-more-about-cargo.html"><strong aria-hidden="true">14.</strong> More about Cargo and Crates.io</a></li><li><ol class="section"><li class="expanded "><a href="ch14-01-release-profiles.html"><strong aria-hidden="true">14.1.</strong> Customizing Builds with Release Profiles</a></li><li class="expanded "><a href="ch14-02-publishing-to-crates-io.html"><strong aria-hidden="true">14.2.</strong> Publishing a Crate to Crates.io</a></li><li class="expanded "><a href="ch14-03-cargo-workspaces.html" class="active"><strong aria-hidden="true">14.3.</strong> Cargo Workspaces</a></li><li class="expanded "><a href="ch14-04-installing-binaries.html"><strong aria-hidden="true">14.4.</strong> Installing Binaries from Crates.io with cargo install</a></li><li class="expanded "><a href="ch14-05-extending-cargo.html"><strong aria-hidden="true">14.5.</strong> Extending Cargo with Custom Commands</a></li></ol></li><li class="expanded "><a href="ch15-00-smart-pointers.html"><strong aria-hidden="true">15.</strong> Smart Pointers</a></li><li><ol class="section"><li class="expanded "><a href="ch15-01-box.html"><strong aria-hidden="true">15.1.</strong> Using Box<T> to Point to Data on the Heap</a></li><li class="expanded "><a href="ch15-02-deref.html"><strong aria-hidden="true">15.2.</strong> Treating Smart Pointers Like Regular References with the Deref Trait</a></li><li class="expanded "><a href="ch15-03-drop.html"><strong aria-hidden="true">15.3.</strong> Running Code on Cleanup with the Drop Trait</a></li><li class="expanded "><a href="ch15-04-rc.html"><strong aria-hidden="true">15.4.</strong> Rc<T>, the Reference Counted Smart Pointer</a></li><li class="expanded "><a href="ch15-05-interior-mutability.html"><strong aria-hidden="true">15.5.</strong> RefCell<T> and the Interior Mutability Pattern</a></li><li class="expanded "><a href="ch15-06-reference-cycles.html"><strong aria-hidden="true">15.6.</strong> Reference Cycles Can Leak Memory</a></li></ol></li><li class="expanded "><a href="ch16-00-concurrency.html"><strong aria-hidden="true">16.</strong> Fearless Concurrency</a></li><li><ol class="section"><li class="expanded "><a href="ch16-01-threads.html"><strong aria-hidden="true">16.1.</strong> Using Threads to Run Code Simultaneously</a></li><li class="expanded "><a href="ch16-02-message-passing.html"><strong aria-hidden="true">16.2.</strong> Using Message Passing to Transfer Data Between Threads</a></li><li class="expanded "><a href="ch16-03-shared-state.html"><strong aria-hidden="true">16.3.</strong> Shared-State Concurrency</a></li><li class="expanded "><a href="ch16-04-extensible-concurrency-sync-and-send.html"><strong aria-hidden="true">16.4.</strong> Extensible Concurrency with the Sync and Send Traits</a></li></ol></li><li class="expanded "><a href="ch17-00-oop.html"><strong aria-hidden="true">17.</strong> Object Oriented Programming Features of Rust</a></li><li><ol class="section"><li class="expanded "><a href="ch17-01-what-is-oo.html"><strong aria-hidden="true">17.1.</strong> Characteristics of Object-Oriented Languages</a></li><li class="expanded "><a href="ch17-02-trait-objects.html"><strong aria-hidden="true">17.2.</strong> Using Trait Objects That Allow for Values of Different Types</a></li><li class="expanded "><a href="ch17-03-oo-design-patterns.html"><strong aria-hidden="true">17.3.</strong> Implementing an Object-Oriented Design Pattern</a></li></ol></li><li class="expanded "><a href="ch18-00-patterns.html"><strong aria-hidden="true">18.</strong> Patterns and Matching</a></li><li><ol class="section"><li class="expanded "><a href="ch18-01-all-the-places-for-patterns.html"><strong aria-hidden="true">18.1.</strong> All the Places Patterns Can Be Used</a></li><li class="expanded "><a href="ch18-02-refutability.html"><strong aria-hidden="true">18.2.</strong> Refutability: Whether a Pattern Might Fail to Match</a></li><li class="expanded "><a href="ch18-03-pattern-syntax.html"><strong aria-hidden="true">18.3.</strong> Pattern Syntax</a></li></ol></li><li class="expanded "><a href="ch19-00-advanced-features.html"><strong aria-hidden="true">19.</strong> Advanced Features</a></li><li><ol class="section"><li class="expanded "><a href="ch19-01-unsafe-rust.html"><strong aria-hidden="true">19.1.</strong> Unsafe Rust</a></li><li class="expanded "><a href="ch19-03-advanced-traits.html"><strong aria-hidden="true">19.2.</strong> Advanced Traits</a></li><li class="expanded "><a href="ch19-04-advanced-types.html"><strong aria-hidden="true">19.3.</strong> Advanced Types</a></li><li class="expanded "><a href="ch19-05-advanced-functions-and-closures.html"><strong aria-hidden="true">19.4.</strong> Advanced Functions and Closures</a></li><li class="expanded "><a href="ch19-06-macros.html"><strong aria-hidden="true">19.5.</strong> Macros</a></li></ol></li><li class="expanded "><a href="ch20-00-final-project-a-web-server.html"><strong aria-hidden="true">20.</strong> Final Project: Building a Multithreaded Web Server</a></li><li><ol class="section"><li class="expanded "><a href="ch20-01-single-threaded.html"><strong aria-hidden="true">20.1.</strong> Building a Single-Threaded Web Server</a></li><li class="expanded "><a href="ch20-02-multithreaded.html"><strong aria-hidden="true">20.2.</strong> Turning Our Single-Threaded Server into a Multithreaded Server</a></li><li class="expanded "><a href="ch20-03-graceful-shutdown-and-cleanup.html"><strong aria-hidden="true">20.3.</strong> Graceful Shutdown and Cleanup</a></li></ol></li><li class="expanded "><a href="appendix-00.html"><strong aria-hidden="true">21.</strong> Appendix</a></li><li><ol class="section"><li class="expanded "><a href="appendix-01-keywords.html"><strong aria-hidden="true">21.1.</strong> A - Keywords</a></li><li class="expanded "><a href="appendix-02-operators.html"><strong aria-hidden="true">21.2.</strong> B - Operators and Symbols</a></li><li class="expanded "><a href="appendix-03-derivable-traits.html"><strong aria-hidden="true">21.3.</strong> C - Derivable Traits</a></li><li class="expanded "><a href="appendix-04-useful-development-tools.html"><strong aria-hidden="true">21.4.</strong> D - Useful Development Tools</a></li><li class="expanded "><a href="appendix-05-editions.html"><strong aria-hidden="true">21.5.</strong> E - Editions</a></li><li class="expanded "><a href="appendix-06-translation.html"><strong aria-hidden="true">21.6.</strong> F - Translations of the Book</a></li><li class="expanded "><a href="appendix-07-nightly-rust.html"><strong aria-hidden="true">21.7.</strong> G - How Rust is Made and “Nightly Rust”</a></li></ol></li></ol>
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<h2><a class="header" href="#cargo-workspaces" id="cargo-workspaces">Cargo Workspaces</a></h2>
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<p>In Chapter 12, we built a package that included a binary crate and a library
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crate. As your project develops, you might find that the library crate
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continues to get bigger and you want to split up your package further into
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multiple library crates. In this situation, Cargo offers a feature called
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<em>workspaces</em> that can help manage multiple related packages that are developed
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in tandem.</p>
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<h3><a class="header" href="#creating-a-workspace" id="creating-a-workspace">Creating a Workspace</a></h3>
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<p>A <em>workspace</em> is a set of packages that share the same <em>Cargo.lock</em> and output
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directory. Let’s make a project using a workspace—we’ll use trivial code so we
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can concentrate on the structure of the workspace. There are multiple ways to
|
||
structure a workspace; we’re going to show one common way. We’ll have a
|
||
workspace containing a binary and two libraries. The binary, which will provide
|
||
the main functionality, will depend on the two libraries. One library will
|
||
provide an <code>add_one</code> function, and a second library an <code>add_two</code> function.
|
||
These three crates will be part of the same workspace. We’ll start by creating
|
||
a new directory for the workspace:</p>
|
||
<pre><code class="language-text">$ mkdir add
|
||
$ cd add
|
||
</code></pre>
|
||
<p>Next, in the <em>add</em> directory, we create the <em>Cargo.toml</em> file that will
|
||
configure the entire workspace. This file won’t have a <code>[package]</code> section or
|
||
the metadata we’ve seen in other <em>Cargo.toml</em> files. Instead, it will start
|
||
with a <code>[workspace]</code> section that will allow us to add members to the workspace
|
||
by specifying the path to our binary crate; in this case, that path is <em>adder</em>:</p>
|
||
<p><span class="filename">Filename: Cargo.toml</span></p>
|
||
<pre><code class="language-toml">[workspace]
|
||
|
||
members = [
|
||
"adder",
|
||
]
|
||
</code></pre>
|
||
<p>Next, we’ll create the <code>adder</code> binary crate by running <code>cargo new</code> within the
|
||
<em>add</em> directory:</p>
|
||
<pre><code class="language-text">$ cargo new adder
|
||
Created binary (application) `adder` project
|
||
</code></pre>
|
||
<p>At this point, we can build the workspace by running <code>cargo build</code>. The files
|
||
in your <em>add</em> directory should look like this:</p>
|
||
<pre><code class="language-text">├── Cargo.lock
|
||
├── Cargo.toml
|
||
├── adder
|
||
│ ├── Cargo.toml
|
||
│ └── src
|
||
│ └── main.rs
|
||
└── target
|
||
</code></pre>
|
||
<p>The workspace has one <em>target</em> directory at the top level for the compiled
|
||
artifacts to be placed into; the <code>adder</code> crate doesn’t have its own <em>target</em>
|
||
directory. Even if we were to run <code>cargo build</code> from inside the <em>adder</em>
|
||
directory, the compiled artifacts would still end up in <em>add/target</em> rather
|
||
than <em>add/adder/target</em>. Cargo structures the <em>target</em> directory in a workspace
|
||
like this because the crates in a workspace are meant to depend on each other.
|
||
If each crate had its own <em>target</em> directory, each crate would have to
|
||
recompile each of the other crates in the workspace to have the artifacts in
|
||
its own <em>target</em> directory. By sharing one <em>target</em> directory, the crates can
|
||
avoid unnecessary rebuilding.</p>
|
||
<h3><a class="header" href="#creating-the-second-crate-in-the-workspace" id="creating-the-second-crate-in-the-workspace">Creating the Second Crate in the Workspace</a></h3>
|
||
<p>Next, let’s create another member crate in the workspace and call it <code>add-one</code>.
|
||
Change the top-level <em>Cargo.toml</em> to specify the <em>add-one</em> path in the
|
||
<code>members</code> list:</p>
|
||
<p><span class="filename">Filename: Cargo.toml</span></p>
|
||
<pre><code class="language-toml">[workspace]
|
||
|
||
members = [
|
||
"adder",
|
||
"add-one",
|
||
]
|
||
</code></pre>
|
||
<p>Then generate a new library crate named <code>add-one</code>:</p>
|
||
<pre><code class="language-text">$ cargo new add-one --lib
|
||
Created library `add-one` project
|
||
</code></pre>
|
||
<p>Your <em>add</em> directory should now have these directories and files:</p>
|
||
<pre><code class="language-text">├── Cargo.lock
|
||
├── Cargo.toml
|
||
├── add-one
|
||
│ ├── Cargo.toml
|
||
│ └── src
|
||
│ └── lib.rs
|
||
├── adder
|
||
│ ├── Cargo.toml
|
||
│ └── src
|
||
│ └── main.rs
|
||
└── target
|
||
</code></pre>
|
||
<p>In the <em>add-one/src/lib.rs</em> file, let’s add an <code>add_one</code> function:</p>
|
||
<p><span class="filename">Filename: add-one/src/lib.rs</span></p>
|
||
<pre><pre class="playpen"><code class="language-rust">
|
||
<span class="boring">#![allow(unused_variables)]
|
||
</span><span class="boring">fn main() {
|
||
</span>pub fn add_one(x: i32) -> i32 {
|
||
x + 1
|
||
}
|
||
<span class="boring">}
|
||
</span></code></pre></pre>
|
||
<p>Now that we have a library crate in the workspace, we can have the binary crate
|
||
<code>adder</code> depend on the library crate <code>add-one</code>. First, we’ll need to add a path
|
||
dependency on <code>add-one</code> to <em>adder/Cargo.toml</em>.</p>
|
||
<p><span class="filename">Filename: adder/Cargo.toml</span></p>
|
||
<pre><code class="language-toml">[dependencies]
|
||
|
||
add-one = { path = "../add-one" }
|
||
</code></pre>
|
||
<p>Cargo doesn’t assume that crates in a workspace will depend on each other, so
|
||
we need to be explicit about the dependency relationships between the crates.</p>
|
||
<p>Next, let’s use the <code>add_one</code> function from the <code>add-one</code> crate in the <code>adder</code>
|
||
crate. Open the <em>adder/src/main.rs</em> file and add a <code>use</code> line at the top to
|
||
bring the new <code>add-one</code> library crate into scope. Then change the <code>main</code>
|
||
function to call the <code>add_one</code> function, as in Listing 14-7.</p>
|
||
<p><span class="filename">Filename: adder/src/main.rs</span></p>
|
||
<pre><code class="language-rust ignore">use add_one;
|
||
|
||
fn main() {
|
||
let num = 10;
|
||
println!("Hello, world! {} plus one is {}!", num, add_one::add_one(num));
|
||
}
|
||
</code></pre>
|
||
<p><span class="caption">Listing 14-7: Using the <code>add-one</code> library crate from the
|
||
<code>adder</code> crate</span></p>
|
||
<p>Let’s build the workspace by running <code>cargo build</code> in the top-level <em>add</em>
|
||
directory!</p>
|
||
<pre><code class="language-text">$ cargo build
|
||
Compiling add-one v0.1.0 (file:///projects/add/add-one)
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.68 secs
|
||
</code></pre>
|
||
<p>To run the binary crate from the <em>add</em> directory, we need to specify which
|
||
package in the workspace we want to use by using the <code>-p</code> argument and the
|
||
package name with <code>cargo run</code>:</p>
|
||
<pre><code class="language-text">$ cargo run -p adder
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running `target/debug/adder`
|
||
Hello, world! 10 plus one is 11!
|
||
</code></pre>
|
||
<p>This runs the code in <em>adder/src/main.rs</em>, which depends on the <code>add-one</code> crate.</p>
|
||
<h4><a class="header" href="#depending-on-an-external-crate-in-a-workspace" id="depending-on-an-external-crate-in-a-workspace">Depending on an External Crate in a Workspace</a></h4>
|
||
<p>Notice that the workspace has only one <em>Cargo.lock</em> file at the top level of
|
||
the workspace rather than having a <em>Cargo.lock</em> in each crate’s directory. This
|
||
ensures that all crates are using the same version of all dependencies. If we
|
||
add the <code>rand</code> crate to the <em>adder/Cargo.toml</em> and <em>add-one/Cargo.toml</em>
|
||
files, Cargo will resolve both of those to one version of <code>rand</code> and record
|
||
that in the one <em>Cargo.lock</em>. Making all crates in the workspace use the same
|
||
dependencies means the crates in the workspace will always be compatible with
|
||
each other. Let’s add the <code>rand</code> crate to the <code>[dependencies]</code> section in the
|
||
<em>add-one/Cargo.toml</em> file to be able to use the <code>rand</code> crate in the <code>add-one</code>
|
||
crate:</p>
|
||
<!-- When updating the version of `rand` used, also update the version of
|
||
`rand` used in these files so they all match:
|
||
* ch02-00-guessing-game-tutorial.md
|
||
* ch07-04-bringing-paths-into-scope-with-the-use-keyword.md
|
||
-->
|
||
<p><span class="filename">Filename: add-one/Cargo.toml</span></p>
|
||
<pre><code class="language-toml">[dependencies]
|
||
rand = "0.5.5"
|
||
</code></pre>
|
||
<p>We can now add <code>use rand;</code> to the <em>add-one/src/lib.rs</em> file, and building the
|
||
whole workspace by running <code>cargo build</code> in the <em>add</em> directory will bring in
|
||
and compile the <code>rand</code> crate:</p>
|
||
<pre><code class="language-text">$ cargo build
|
||
Updating crates.io index
|
||
Downloaded rand v0.5.5
|
||
--snip--
|
||
Compiling rand v0.5.5
|
||
Compiling add-one v0.1.0 (file:///projects/add/add-one)
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 10.18 secs
|
||
</code></pre>
|
||
<p>The top-level <em>Cargo.lock</em> now contains information about the dependency of
|
||
<code>add-one</code> on <code>rand</code>. However, even though <code>rand</code> is used somewhere in the
|
||
workspace, we can’t use it in other crates in the workspace unless we add
|
||
<code>rand</code> to their <em>Cargo.toml</em> files as well. For example, if we add <code>use rand;</code>
|
||
to the <em>adder/src/main.rs</em> file for the <code>adder</code> crate, we’ll get an error:</p>
|
||
<pre><code class="language-text">$ cargo build
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
error: use of unstable library feature 'rand': use `rand` from crates.io (see
|
||
issue #27703)
|
||
--> adder/src/main.rs:1:1
|
||
|
|
||
1 | use rand;
|
||
</code></pre>
|
||
<p>To fix this, edit the <em>Cargo.toml</em> file for the <code>adder</code> crate and indicate that
|
||
<code>rand</code> is a dependency for that crate as well. Building the <code>adder</code> crate will
|
||
add <code>rand</code> to the list of dependencies for <code>adder</code> in <em>Cargo.lock</em>, but no
|
||
additional copies of <code>rand</code> will be downloaded. Cargo has ensured that every
|
||
crate in the workspace using the <code>rand</code> crate will be using the same version.
|
||
Using the same version of <code>rand</code> across the workspace saves space because we
|
||
won’t have multiple copies and ensures that the crates in the workspace will be
|
||
compatible with each other.</p>
|
||
<h4><a class="header" href="#adding-a-test-to-a-workspace" id="adding-a-test-to-a-workspace">Adding a Test to a Workspace</a></h4>
|
||
<p>For another enhancement, let’s add a test of the <code>add_one::add_one</code> function
|
||
within the <code>add_one</code> crate:</p>
|
||
<p><span class="filename">Filename: add-one/src/lib.rs</span></p>
|
||
<pre><pre class="playpen"><code class="language-rust">
|
||
<span class="boring">#![allow(unused_variables)]
|
||
</span><span class="boring">fn main() {
|
||
</span>pub fn add_one(x: i32) -> i32 {
|
||
x + 1
|
||
}
|
||
|
||
#[cfg(test)]
|
||
mod tests {
|
||
use super::*;
|
||
|
||
#[test]
|
||
fn it_works() {
|
||
assert_eq!(3, add_one(2));
|
||
}
|
||
}
|
||
<span class="boring">}
|
||
</span></code></pre></pre>
|
||
<p>Now run <code>cargo test</code> in the top-level <em>add</em> directory:</p>
|
||
<pre><code class="language-text">$ cargo test
|
||
Compiling add-one v0.1.0 (file:///projects/add/add-one)
|
||
Compiling adder v0.1.0 (file:///projects/add/adder)
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.27 secs
|
||
Running target/debug/deps/add_one-f0253159197f7841
|
||
|
||
running 1 test
|
||
test tests::it_works ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Running target/debug/deps/adder-f88af9d2cc175a5e
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Doc-tests add-one
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>The first section of the output shows that the <code>it_works</code> test in the <code>add-one</code>
|
||
crate passed. The next section shows that zero tests were found in the <code>adder</code>
|
||
crate, and then the last section shows zero documentation tests were found in
|
||
the <code>add-one</code> crate. Running <code>cargo test</code> in a workspace structured like this
|
||
one will run the tests for all the crates in the workspace.</p>
|
||
<p>We can also run tests for one particular crate in a workspace from the
|
||
top-level directory by using the <code>-p</code> flag and specifying the name of the crate
|
||
we want to test:</p>
|
||
<pre><code class="language-text">$ cargo test -p add-one
|
||
Finished dev [unoptimized + debuginfo] target(s) in 0.0 secs
|
||
Running target/debug/deps/add_one-b3235fea9a156f74
|
||
|
||
running 1 test
|
||
test tests::it_works ... ok
|
||
|
||
test result: ok. 1 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
|
||
Doc-tests add-one
|
||
|
||
running 0 tests
|
||
|
||
test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out
|
||
</code></pre>
|
||
<p>This output shows <code>cargo test</code> only ran the tests for the <code>add-one</code> crate and
|
||
didn’t run the <code>adder</code> crate tests.</p>
|
||
<p>If you publish the crates in the workspace to <a href="https://crates.io/">crates.io</a>,
|
||
each crate in the workspace will need to be published separately. The <code>cargo publish</code> command does not have an <code>--all</code> flag or a <code>-p</code> flag, so you must
|
||
change to each crate’s directory and run <code>cargo publish</code> on each crate in the
|
||
workspace to publish the crates.</p>
|
||
<p>For additional practice, add an <code>add-two</code> crate to this workspace in a similar
|
||
way as the <code>add-one</code> crate!</p>
|
||
<p>As your project grows, consider using a workspace: it’s easier to understand
|
||
smaller, individual components than one big blob of code. Furthermore, keeping
|
||
the crates in a workspace can make coordination between them easier if they are
|
||
often changed at the same time.</p>
|
||
|
||
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|
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