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<ol class="chapter"><li class="affix"><a href="title-page.html">The Rust Programming Language</a></li><li class="affix"><a href="foreword.html">Foreword</a></li><li class="affix"><a href="ch00-00-introduction.html">Introduction</a></li><li><a href="ch01-00-getting-started.html"><strong aria-hidden="true">1.</strong> Getting Started</a></li><li><ol class="section"><li><a href="ch01-01-installation.html"><strong aria-hidden="true">1.1.</strong> Installation</a></li><li><a href="ch01-02-hello-world.html"><strong aria-hidden="true">1.2.</strong> Hello, World!</a></li><li><a href="ch01-03-hello-cargo.html"><strong aria-hidden="true">1.3.</strong> Hello, Cargo!</a></li></ol></li><li><a href="ch02-00-guessing-game-tutorial.html"><strong aria-hidden="true">2.</strong> Programming a Guessing Game</a></li><li><a href="ch03-00-common-programming-concepts.html"><strong aria-hidden="true">3.</strong> Common Programming Concepts</a></li><li><ol class="section"><li><a href="ch03-01-variables-and-mutability.html"><strong aria-hidden="true">3.1.</strong> Variables and Mutability</a></li><li><a href="ch03-02-data-types.html"><strong aria-hidden="true">3.2.</strong> Data Types</a></li><li><a href="ch03-03-how-functions-work.html"><strong aria-hidden="true">3.3.</strong> Functions</a></li><li><a href="ch03-04-comments.html"><strong aria-hidden="true">3.4.</strong> Comments</a></li><li><a href="ch03-05-control-flow.html"><strong aria-hidden="true">3.5.</strong> Control Flow</a></li></ol></li><li><a href="ch04-00-understanding-ownership.html"><strong aria-hidden="true">4.</strong> Understanding Ownership</a></li><li><ol class="section"><li><a href="ch04-01-what-is-ownership.html"><strong aria-hidden="true">4.1.</strong> What is Ownership?</a></li><li><a href="ch04-02-references-and-borrowing.html"><strong aria-hidden="true">4.2.</strong> References and Borrowing</a></li><li><a href="ch04-03-slices.html"><strong aria-hidden="true">4.3.</strong> The Slice Type</a></li></ol></li><li><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><a href="ch05-01-defining-structs.html"><strong aria-hidden="true">5.1.</strong> Defining and Instantiating Structs</a></li><li><a href="ch05-02-example-structs.html"><strong aria-hidden="true">5.2.</strong> An Example Program Using Structs</a></li><li><a href="ch05-03-method-syntax.html"><strong aria-hidden="true">5.3.</strong> Method Syntax</a></li></ol></li><li><a href="ch06-00-enums.html"><strong aria-hidden="true">6.</strong> Enums and Pattern Matching</a></li><li><ol class="section"><li><a href="ch06-01-defining-an-enum.html"><strong aria-hidden="true">6.1.</strong> Defining an Enum</a></li><li><a href="ch06-02-match.html"><strong aria-hidden="true">6.2.</strong> The match Control Flow Operator</a></li><li><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><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><a href="ch07-01-packages-and-crates.html"><strong aria-hidden="true">7.1.</strong> Packages and Crates</a></li><li><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><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><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><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><a href="ch08-00-common-collections.html"><strong aria-hidden="true">8.</strong> Common Collections</a></li><li><ol class="section"><li><a href="ch08-01-vectors.html"><strong aria-hidden="true">8.1.</strong> Storing Lists of Values with Vectors</a></li><li><a href="ch08-02-strings.html"><strong aria-hidden="true">8.2.</strong> Storing UTF-8 Encoded Text with Strings</a></li><li><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><a href="ch09-00-error-handling.html"><strong aria-hidden="true">9.</strong> Error Handling</a></li><li><ol class="section"><li><a href="ch09-01-unrecoverable-errors-with-panic.html"><strong aria-hidden="true">9.1.</strong> Unrecoverable Errors with panic!</a></li><li><a href="ch09-02-recoverable-errors-with-result.html"><strong aria-hidden="true">9.2.</strong> Recoverable Errors with Result</a></li><li><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><a href="ch10-00-generics.html"><strong aria-hidden="true">10.</strong> Generic Types, Traits, and Lifetimes</a></li><li><ol class="section"><li><a href="ch10-01-syntax.html"><strong aria-hidden="true">10.1.</strong> Generic Data Types</a></li><li><a href="ch10-02-traits.html"><strong aria-hidden="true">10.2.</strong> Traits: Defining Shared Behavior</a></li><li><a href="ch10-03-lifetime-syntax.html"><strong aria-hidden="true">10.3.</strong> Validating References with Lifetimes</a></li></ol></li><li><a href="ch11-00-testing.html"><strong aria-hidden="true">11.</strong> Writing Automated Tests</a></li><li><ol class="section"><li><a href="ch11-01-writing-tests.html"><strong aria-hidden="true">11.1.</strong> How to Write Tests</a></li><li><a href="ch11-02-running-tests.html"><strong aria-hidden="true">11.2.</strong> Controlling How Tests Are Run</a></li><li><a href="ch11-03-test-organization.html"><strong aria-hidden="true">11.3.</strong> Test Organization</a></li></ol></li><li><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><a href="ch12-01-accepting-command-line-arguments.html"><strong aria-hidden="true">12.1.</strong> Accepting Command Line Arguments</a></li><li><a href="ch12-02-reading-a-file.html"><strong aria-hidden="true">12.2.</strong> Reading a File</a></li><li><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><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><a href="ch12-05-working-with-environment-variables.html"><strong aria-hidden="true">12.5.</strong> Working with Environment Variables</a></li><li><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><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><a href="ch13-01-closures.html"><strong aria-hidden="true">13.1.</strong> Closures: Anonymous Functions that Can Capture Their Environment</a></li><li><a href="ch13-02-iterators.html"><strong aria-hidden="true">13.2.</strong> Processing a Series of Items with Iterators</a></li><li><a href="ch13-03-improving-our-io-project.html"><strong aria-hidden="true">13.3.</strong> Improving Our I/O Project</a></li><li><a href="ch13-04-performance.html"><strong aria-hidden="true">13.4.</strong> Comparing Performance: Loops vs. Iterators</a></li></ol></li><li><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><a href="ch14-01-release-profiles.html"><strong aria-hidden="true">14.1.</strong> Customizing Builds with Release Profiles</a></li><li><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><a href="ch14-03-cargo-workspaces.html"><strong aria-hidden="true">14.3.</strong> Cargo Workspaces</a></li><li><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><a href="ch14-05-extending-cargo.html"><strong aria-hidden="true">14.5.</strong> Extending Cargo with Custom Commands</a></li></ol></li><li><a href="ch15-00-smart-pointers.html"><strong aria-hidden="true">15.</strong> Smart Pointers</a></li><li><ol class="section"><li><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><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><a href="ch15-03-drop.html"><strong aria-hidden="true">15.3.</strong> Running Code on Cleanup with the Drop Trait</a></li><li><a href="ch15-04-rc.html"><strong aria-hidden="true">15.4.</strong> Rc<T>, the Reference Counted Smart Pointer</a></li><li><a href="ch15-05-interior-mutability.html"><strong aria-hidden="true">15.5.</strong> RefCell<T> and the Interior Mutability Pattern</a></li><li><a href="ch15-06-reference-cycles.html"><strong aria-hidden="true">15.6.</strong> Reference Cycles Can Leak Memory</a></li></ol></li><li><a href="ch16-00-concurrency.html"><strong aria-hidden="true">16.</strong> Fearless Concurrency</a></li><li><ol class="section"><li><a href="ch16-01-threads.html"><strong aria-hidden="true">16.1.</strong> Using Threads to Run Code Simultaneously</a></li><li><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><a href="ch16-03-shared-state.html"><strong aria-hidden="true">16.3.</strong> Shared-State Concurrency</a></li><li><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><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><a href="ch17-01-what-is-oo.html"><strong aria-hidden="true">17.1.</strong> Characteristics of Object-Oriented Languages</a></li><li><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><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><a href="ch18-00-patterns.html"><strong aria-hidden="true">18.</strong> Patterns and Matching</a></li><li><ol class="section"><li><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><a href="ch18-02-refutability.html"><strong aria-hidden="true">18.2.</strong> Refutability: Whether a Pattern Might Fail to Match</a></li><li><a href="ch18-03-pattern-syntax.html"><strong aria-hidden="true">18.3.</strong> Pattern Syntax</a></li></ol></li><li><a href="ch19-00-advanced-features.html"><strong aria-hidden="true">19.</strong> Advanced Features</a></li><li><ol class="section"><li><a href="ch19-01-unsafe-rust.html"><strong aria-hidden="true">19.1.</strong> Unsafe Rust</a></li><li><a href="ch19-02-advanced-lifetimes.html"><strong aria-hidden="true">19.2.</strong> Advanced Lifetimes</a></li><li><a href="ch19-03-advanced-traits.html"><strong aria-hidden="true">19.3.</strong> Advanced Traits</a></li><li><a href="ch19-04-advanced-types.html"><strong aria-hidden="true">19.4.</strong> Advanced Types</a></li><li><a href="ch19-05-advanced-functions-and-closures.html"><strong aria-hidden="true">19.5.</strong> Advanced Functions and Closures</a></li><li><a href="ch19-06-macros.html"><strong aria-hidden="true">19.6.</strong> Macros</a></li></ol></li><li><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><a href="ch20-01-single-threaded.html"><strong aria-hidden="true">20.1.</strong> Building a Single-Threaded Web Server</a></li><li><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><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><a href="appendix-00.html"><strong aria-hidden="true">21.</strong> Appendix</a></li><li><ol class="section"><li><a href="appendix-01-keywords.html"><strong aria-hidden="true">21.1.</strong> A - Keywords</a></li><li><a href="appendix-02-operators.html" class="active"><strong aria-hidden="true">21.2.</strong> B - Operators and Symbols</a></li><li><a href="appendix-03-derivable-traits.html"><strong aria-hidden="true">21.3.</strong> C - Derivable Traits</a></li><li><a href="appendix-04-useful-development-tools.html"><strong aria-hidden="true">21.4.</strong> D - Useful Development Tools</a></li><li><a href="appendix-05-editions.html"><strong aria-hidden="true">21.5.</strong> E - Editions</a></li><li><a href="appendix-06-translation.html"><strong aria-hidden="true">21.6.</strong> F - Translations of the Book</a></li><li><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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<a class="header" href="appendix-02-operators.html#appendix-b-operators-and-symbols" id="appendix-b-operators-and-symbols"><h2>Appendix B: Operators and Symbols</h2></a>
<p>This appendix contains a glossary of Rust’s syntax, including operators and
other symbols that appear by themselves or in the context of paths, generics,
trait bounds, macros, attributes, comments, tuples, and brackets.</p>
<a class="header" href="appendix-02-operators.html#operators" id="operators"><h3>Operators</h3></a>
<p>Table B-1 contains the operators in Rust, an example of how the operator would
appear in context, a short explanation, and whether that operator is
overloadable. If an operator is overloadable, the relevant trait to use to
overload that operator is listed.</p>
<p><span class="caption">Table B-1: Operators</span></p>
<table><thead><tr><th> Operator </th><th> Example </th><th> Explanation </th><th> Overloadable? </th></tr></thead><tbody>
<tr><td> <code>!</code> </td><td> <code>ident!(...)</code>, <code>ident!{...}</code>, <code>ident![...]</code> </td><td> Macro expansion </td><td> </td></tr>
<tr><td> <code>!</code> </td><td> <code>!expr</code> </td><td> Bitwise or logical complement </td><td> <code>Not</code> </td></tr>
<tr><td> <code>!=</code> </td><td> <code>var != expr</code> </td><td> Nonequality comparison </td><td> <code>PartialEq</code> </td></tr>
<tr><td> <code>%</code> </td><td> <code>expr % expr</code> </td><td> Arithmetic remainder </td><td> <code>Rem</code> </td></tr>
<tr><td> <code>%=</code> </td><td> <code>var %= expr</code> </td><td> Arithmetic remainder and assignment </td><td> <code>RemAssign</code> </td></tr>
<tr><td> <code>&</code> </td><td> <code>&expr</code>, <code>&mut expr</code> </td><td> Borrow </td><td> </td></tr>
<tr><td> <code>&</code> </td><td> <code>&type</code>, <code>&mut type</code>, <code>&'a type</code>, <code>&'a mut type</code> </td><td> Borrowed pointer type </td><td> </td></tr>
<tr><td> <code>&</code> </td><td> <code>expr & expr</code> </td><td> Bitwise AND </td><td> <code>BitAnd</code> </td></tr>
<tr><td> <code>&=</code> </td><td> <code>var &= expr</code> </td><td> Bitwise AND and assignment </td><td> <code>BitAndAssign</code> </td></tr>
<tr><td> <code>&&</code> </td><td> <code>expr && expr</code> </td><td> Logical AND </td><td> </td></tr>
<tr><td> <code>*</code> </td><td> <code>expr * expr</code> </td><td> Arithmetic multiplication </td><td> <code>Mul</code> </td></tr>
<tr><td> <code>*=</code> </td><td> <code>var *= expr</code> </td><td> Arithmetic multiplication and assignment </td><td> <code>MulAssign</code> </td></tr>
<tr><td> <code>*</code> </td><td> <code>*expr</code> </td><td> Dereference </td><td> </td></tr>
<tr><td> <code>*</code> </td><td> <code>*const type</code>, <code>*mut type</code> </td><td> Raw pointer </td><td> </td></tr>
<tr><td> <code>+</code> </td><td> <code>trait + trait</code>, <code>'a + trait</code> </td><td> Compound type constraint </td><td> </td></tr>
<tr><td> <code>+</code> </td><td> <code>expr + expr</code> </td><td> Arithmetic addition </td><td> <code>Add</code> </td></tr>
<tr><td> <code>+=</code> </td><td> <code>var += expr</code> </td><td> Arithmetic addition and assignment </td><td> <code>AddAssign</code> </td></tr>
<tr><td> <code>,</code> </td><td> <code>expr, expr</code> </td><td> Argument and element separator </td><td> </td></tr>
<tr><td> <code>-</code> </td><td> <code>- expr</code> </td><td> Arithmetic negation </td><td> <code>Neg</code> </td></tr>
<tr><td> <code>-</code> </td><td> <code>expr - expr</code> </td><td> Arithmetic subtraction </td><td> <code>Sub</code> </td></tr>
<tr><td> <code>-=</code> </td><td> <code>var -= expr</code> </td><td> Arithmetic subtraction and assignment </td><td> <code>SubAssign</code> </td></tr>
<tr><td> <code>-></code> </td><td> <code>fn(...) -> type</code>, <code>|...| -> type</code> </td><td> Function and closure return type </td><td> </td></tr>
<tr><td> <code>.</code> </td><td> <code>expr.ident</code> </td><td> Member access </td><td> </td></tr>
<tr><td> <code>..</code> </td><td> <code>..</code>, <code>expr..</code>, <code>..expr</code>, <code>expr..expr</code> </td><td> Right-exclusive range literal </td><td> </td></tr>
<tr><td> <code>..=</code> </td><td> <code>..=expr</code>, <code>expr..=expr</code> </td><td> Right-inclusive range literal </td><td> </td></tr>
<tr><td> <code>..</code> </td><td> <code>..expr</code> </td><td> Struct literal update syntax </td><td> </td></tr>
<tr><td> <code>..</code> </td><td> <code>variant(x, ..)</code>, <code>struct_type { x, .. }</code> </td><td> “And the rest” pattern binding </td><td> </td></tr>
<tr><td> <code>...</code> </td><td> <code>expr...expr</code> </td><td> In a pattern: inclusive range pattern </td><td> </td></tr>
<tr><td> <code>/</code> </td><td> <code>expr / expr</code> </td><td> Arithmetic division </td><td> <code>Div</code> </td></tr>
<tr><td> <code>/=</code> </td><td> <code>var /= expr</code> </td><td> Arithmetic division and assignment </td><td> <code>DivAssign</code> </td></tr>
<tr><td> <code>:</code> </td><td> <code>pat: type</code>, <code>ident: type</code> </td><td> Constraints </td><td> </td></tr>
<tr><td> <code>:</code> </td><td> <code>ident: expr</code> </td><td> Struct field initializer </td><td> </td></tr>
<tr><td> <code>:</code> </td><td> <code>'a: loop {...}</code> </td><td> Loop label </td><td> </td></tr>
<tr><td> <code>;</code> </td><td> <code>expr;</code> </td><td> Statement and item terminator </td><td> </td></tr>
<tr><td> <code>;</code> </td><td> <code>[...; len]</code> </td><td> Part of fixed-size array syntax </td><td> </td></tr>
<tr><td> <code><<</code> </td><td> <code>expr << expr</code> </td><td> Left-shift </td><td> <code>Shl</code> </td></tr>
<tr><td> <code><<=</code> </td><td> <code>var <<= expr</code> </td><td> Left-shift and assignment </td><td> <code>ShlAssign</code> </td></tr>
<tr><td> <code><</code> </td><td> <code>expr < expr</code> </td><td> Less than comparison </td><td> <code>PartialOrd</code> </td></tr>
<tr><td> <code><=</code> </td><td> <code>expr <= expr</code> </td><td> Less than or equal to comparison </td><td> <code>PartialOrd</code> </td></tr>
<tr><td> <code>=</code> </td><td> <code>var = expr</code>, <code>ident = type</code> </td><td> Assignment/equivalence </td><td> </td></tr>
<tr><td> <code>==</code> </td><td> <code>expr == expr</code> </td><td> Equality comparison </td><td> <code>PartialEq</code> </td></tr>
<tr><td> <code>=></code> </td><td> <code>pat => expr</code> </td><td> Part of match arm syntax </td><td> </td></tr>
<tr><td> <code>></code> </td><td> <code>expr > expr</code> </td><td> Greater than comparison </td><td> <code>PartialOrd</code> </td></tr>
<tr><td> <code>>=</code> </td><td> <code>expr >= expr</code> </td><td> Greater than or equal to comparison </td><td> <code>PartialOrd</code> </td></tr>
<tr><td> <code>>></code> </td><td> <code>expr >> expr</code> </td><td> Right-shift </td><td> <code>Shr</code> </td></tr>
<tr><td> <code>>>=</code> </td><td> <code>var >>= expr</code> </td><td> Right-shift and assignment </td><td> <code>ShrAssign</code> </td></tr>
<tr><td> <code>@</code> </td><td> <code>ident @ pat</code> </td><td> Pattern binding </td><td> </td></tr>
<tr><td> <code>^</code> </td><td> <code>expr ^ expr</code> </td><td> Bitwise exclusive OR </td><td> <code>BitXor</code> </td></tr>
<tr><td> <code>^=</code> </td><td> <code>var ^= expr</code> </td><td> Bitwise exclusive OR and assignment </td><td> <code>BitXorAssign</code> </td></tr>
<tr><td> <code>|</code> </td><td> <code>pat | pat</code> </td><td> Pattern alternatives </td><td> </td></tr>
<tr><td> <code>|</code> </td><td> <code>expr | expr</code> </td><td> Bitwise OR </td><td> <code>BitOr</code> </td></tr>
<tr><td> <code>|=</code> </td><td> <code>var |= expr</code> </td><td> Bitwise OR and assignment </td><td> <code>BitOrAssign</code> </td></tr>
<tr><td> <code>||</code> </td><td> <code>expr || expr</code> </td><td> Logical OR </td><td> </td></tr>
<tr><td> <code>?</code> </td><td> <code>expr?</code> </td><td> Error propagation </td><td> </td></tr>
</tbody></table>
<a class="header" href="appendix-02-operators.html#non-operator-symbols" id="non-operator-symbols"><h3>Non-operator Symbols</h3></a>
<p>The following list contains all non-letters that don’t function as operators;
that is, they don’t behave like a function or method call.</p>
<p>Table B-2 shows symbols that appear on their own and are valid in a variety of
locations.</p>
<p><span class="caption">Table B-2: Stand-Alone Syntax</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>'ident</code> </td><td> Named lifetime or loop label </td></tr>
<tr><td> <code>...u8</code>, <code>...i32</code>, <code>...f64</code>, <code>...usize</code>, etc. </td><td> Numeric literal of specific type </td></tr>
<tr><td> <code>"..."</code> </td><td> String literal </td></tr>
<tr><td> <code>r"..."</code>, <code>r#"..."#</code>, <code>r##"..."##</code>, etc. </td><td> Raw string literal, escape characters not processed </td></tr>
<tr><td> <code>b"..."</code> </td><td> Byte string literal; constructs a <code>[u8]</code> instead of a string </td></tr>
<tr><td> <code>br"..."</code>, <code>br#"..."#</code>, <code>br##"..."##</code>, etc. </td><td> Raw byte string literal, combination of raw and byte string literal </td></tr>
<tr><td> <code>'...'</code> </td><td> Character literal </td></tr>
<tr><td> <code>b'...'</code> </td><td> ASCII byte literal </td></tr>
<tr><td> <code>|...| expr</code> </td><td> Closure </td></tr>
<tr><td> <code>!</code> </td><td> Always empty bottom type for diverging functions </td></tr>
<tr><td> <code>_</code> </td><td> “Ignored” pattern binding; also used to make integer literals readable </td></tr>
</tbody></table>
<p>Table B-3 shows symbols that appear in the context of a path through the module
hierarchy to an item.</p>
<p><span class="caption">Table B-3: Path-Related Syntax</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>ident::ident</code> </td><td> Namespace path </td></tr>
<tr><td> <code>::path</code> </td><td> Path relative to the crate root (i.e., an explicitly absolute path) </td></tr>
<tr><td> <code>self::path</code> </td><td> Path relative to the current module (i.e., an explicitly relative path).</td></tr>
<tr><td> <code>super::path</code> </td><td> Path relative to the parent of the current module </td></tr>
<tr><td> <code>type::ident</code>, <code><type as trait>::ident</code> </td><td> Associated constants, functions, and types </td></tr>
<tr><td> <code><type>::...</code> </td><td> Associated item for a type that cannot be directly named (e.g., <code><&T>::...</code>, <code><[T]>::...</code>, etc.) </td></tr>
<tr><td> <code>trait::method(...)</code> </td><td> Disambiguating a method call by naming the trait that defines it </td></tr>
<tr><td> <code>type::method(...)</code> </td><td> Disambiguating a method call by naming the type for which it’s defined </td></tr>
<tr><td> <code><type as trait>::method(...)</code> </td><td> Disambiguating a method call by naming the trait and type </td></tr>
</tbody></table>
<p>Table B-4 shows symbols that appear in the context of using generic type
parameters.</p>
<p><span class="caption">Table B-4: Generics</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>path<...></code> </td><td> Specifies parameters to generic type in a type (e.g., <code>Vec<u8></code>) </td></tr>
<tr><td> <code>path::<...></code>, <code>method::<...></code> </td><td> Specifies parameters to generic type, function, or method in an expression; often referred to as turbofish (e.g., <code>"42".parse::<i32>()</code>) </td></tr>
<tr><td> <code>fn ident<...> ...</code> </td><td> Define generic function </td></tr>
<tr><td> <code>struct ident<...> ...</code> </td><td> Define generic structure </td></tr>
<tr><td> <code>enum ident<...> ...</code> </td><td> Define generic enumeration </td></tr>
<tr><td> <code>impl<...> ...</code> </td><td> Define generic implementation </td></tr>
<tr><td> <code>for<...> type</code> </td><td> Higher-ranked lifetime bounds </td></tr>
<tr><td> <code>type<ident=type></code> </td><td> A generic type where one or more associated types have specific assignments (e.g., <code>Iterator<Item=T></code>) </td></tr>
</tbody></table>
<p>Table B-5 shows symbols that appear in the context of constraining generic type
parameters with trait bounds.</p>
<p><span class="caption">Table B-5: Trait Bound Constraints</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>T: U</code> </td><td> Generic parameter <code>T</code> constrained to types that implement <code>U</code> </td></tr>
<tr><td> <code>T: 'a</code> </td><td> Generic type <code>T</code> must outlive lifetime <code>'a</code> (meaning the type cannot transitively contain any references with lifetimes shorter than <code>'a</code>) </td></tr>
<tr><td> <code>T : 'static</code> </td><td> Generic type <code>T</code> contains no borrowed references other than <code>'static</code> ones </td></tr>
<tr><td> <code>'b: 'a</code> </td><td> Generic lifetime <code>'b</code> must outlive lifetime <code>'a</code> </td></tr>
<tr><td> <code>T: ?Sized</code> </td><td> Allow generic type parameter to be a dynamically sized type </td></tr>
<tr><td> <code>'a + trait</code>, <code>trait + trait</code> </td><td> Compound type constraint </td></tr>
</tbody></table>
<p>Table B-6 shows symbols that appear in the context of calling or defining
macros and specifying attributes on an item.</p>
<p><span class="caption">Table B-6: Macros and Attributes</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>#[meta]</code> </td><td> Outer attribute </td></tr>
<tr><td> <code>#![meta]</code> </td><td> Inner attribute </td></tr>
<tr><td> <code>$ident</code> </td><td> Macro substitution </td></tr>
<tr><td> <code>$ident:kind</code> </td><td> Macro capture </td></tr>
<tr><td> <code>$(…)…</code> </td><td> Macro repetition </td></tr>
</tbody></table>
<p>Table B-7 shows symbols that create comments.</p>
<p><span class="caption">Table B-7: Comments</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>//</code> </td><td> Line comment </td></tr>
<tr><td> <code>//!</code> </td><td> Inner line doc comment </td></tr>
<tr><td> <code>///</code> </td><td> Outer line doc comment </td></tr>
<tr><td> <code>/*...*/</code> </td><td> Block comment </td></tr>
<tr><td> <code>/*!...*/</code> </td><td> Inner block doc comment </td></tr>
<tr><td> <code>/**...*/</code> </td><td> Outer block doc comment </td></tr>
</tbody></table>
<p>Table B-8 shows symbols that appear in the context of using tuples.</p>
<p><span class="caption">Table B-8: Tuples</span></p>
<table><thead><tr><th> Symbol </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>()</code> </td><td> Empty tuple (aka unit), both literal and type </td></tr>
<tr><td> <code>(expr)</code> </td><td> Parenthesized expression </td></tr>
<tr><td> <code>(expr,)</code> </td><td> Single-element tuple expression </td></tr>
<tr><td> <code>(type,)</code> </td><td> Single-element tuple type </td></tr>
<tr><td> <code>(expr, ...)</code> </td><td> Tuple expression </td></tr>
<tr><td> <code>(type, ...)</code> </td><td> Tuple type </td></tr>
<tr><td> <code>expr(expr, ...)</code> </td><td> Function call expression; also used to initialize tuple <code>struct</code>s and tuple <code>enum</code> variants </td></tr>
<tr><td> <code>ident!(...)</code>, <code>ident!{...}</code>, <code>ident![...]</code> </td><td> Macro invocation </td></tr>
<tr><td> <code>expr.0</code>, <code>expr.1</code>, etc. </td><td> Tuple indexing </td></tr>
</tbody></table>
<p>Table B-9 shows the contexts in which curly braces are used.</p>
<p><span class="caption">Table B-9: Curly Brackets</span></p>
<table><thead><tr><th> Context </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>{...}</code> </td><td> Block expression </td></tr>
<tr><td> <code>Type {...}</code> </td><td> <code>struct</code> literal </td></tr>
</tbody></table>
<p>Table B-10 shows the contexts in which square brackets are used.</p>
<p><span class="caption">Table B-10: Square Brackets</span></p>
<table><thead><tr><th> Context </th><th> Explanation </th></tr></thead><tbody>
<tr><td> <code>[...]</code> </td><td> Array literal </td></tr>
<tr><td> <code>[expr; len]</code> </td><td> Array literal containing <code>len</code> copies of <code>expr</code> </td></tr>
<tr><td> <code>[type; len]</code> </td><td> Array type containing <code>len</code> instances of <code>type</code> </td></tr>
<tr><td> <code>expr[expr]</code> </td><td> Collection indexing. Overloadable (<code>Index</code>, <code>IndexMut</code>) </td></tr>
<tr><td> <code>expr[..]</code>, <code>expr[a..]</code>, <code>expr[..b]</code>, <code>expr[a..b]</code> </td><td> Collection indexing pretending to be collection slicing, using <code>Range</code>, <code>RangeFrom</code>, <code>RangeTo</code>, or <code>RangeFull</code> as the “index” </td></tr>
</tbody></table>
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