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<title>Syntax Index - The Rust Programming Language</title>
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<ol class="chapter"><li class="affix"><a href="README.html">Introduction</a></li><li><a href="getting-started.html"><strong aria-hidden="true">1.</strong> Getting Started</a></li><li><a href="guessing-game.html"><strong aria-hidden="true">2.</strong> Tutorial: Guessing Game</a></li><li><a href="syntax-and-semantics.html"><strong aria-hidden="true">3.</strong> Syntax and Semantics</a></li><li><ol class="section"><li><a href="variable-bindings.html"><strong aria-hidden="true">3.1.</strong> Variable Bindings</a></li><li><a href="functions.html"><strong aria-hidden="true">3.2.</strong> Functions</a></li><li><a href="primitive-types.html"><strong aria-hidden="true">3.3.</strong> Primitive Types</a></li><li><a href="comments.html"><strong aria-hidden="true">3.4.</strong> Comments</a></li><li><a href="if.html"><strong aria-hidden="true">3.5.</strong> if</a></li><li><a href="loops.html"><strong aria-hidden="true">3.6.</strong> Loops</a></li><li><a href="vectors.html"><strong aria-hidden="true">3.7.</strong> Vectors</a></li><li><a href="ownership.html"><strong aria-hidden="true">3.8.</strong> Ownership</a></li><li><a href="references-and-borrowing.html"><strong aria-hidden="true">3.9.</strong> References and Borrowing</a></li><li><a href="lifetimes.html"><strong aria-hidden="true">3.10.</strong> Lifetimes</a></li><li><a href="mutability.html"><strong aria-hidden="true">3.11.</strong> Mutability</a></li><li><a href="structs.html"><strong aria-hidden="true">3.12.</strong> Structs</a></li><li><a href="enums.html"><strong aria-hidden="true">3.13.</strong> Enums</a></li><li><a href="match.html"><strong aria-hidden="true">3.14.</strong> Match</a></li><li><a href="patterns.html"><strong aria-hidden="true">3.15.</strong> Patterns</a></li><li><a href="method-syntax.html"><strong aria-hidden="true">3.16.</strong> Method Syntax</a></li><li><a href="strings.html"><strong aria-hidden="true">3.17.</strong> Strings</a></li><li><a href="generics.html"><strong aria-hidden="true">3.18.</strong> Generics</a></li><li><a href="traits.html"><strong aria-hidden="true">3.19.</strong> Traits</a></li><li><a href="drop.html"><strong aria-hidden="true">3.20.</strong> Drop</a></li><li><a href="if-let.html"><strong aria-hidden="true">3.21.</strong> if let</a></li><li><a href="trait-objects.html"><strong aria-hidden="true">3.22.</strong> Trait Objects</a></li><li><a href="closures.html"><strong aria-hidden="true">3.23.</strong> Closures</a></li><li><a href="ufcs.html"><strong aria-hidden="true">3.24.</strong> Universal Function Call Syntax</a></li><li><a href="crates-and-modules.html"><strong aria-hidden="true">3.25.</strong> Crates and Modules</a></li><li><a href="const-and-static.html"><strong aria-hidden="true">3.26.</strong> const and static</a></li><li><a href="attributes.html"><strong aria-hidden="true">3.27.</strong> Attributes</a></li><li><a href="type-aliases.html"><strong aria-hidden="true">3.28.</strong> type aliases</a></li><li><a href="casting-between-types.html"><strong aria-hidden="true">3.29.</strong> Casting between types</a></li><li><a href="associated-types.html"><strong aria-hidden="true">3.30.</strong> Associated Types</a></li><li><a href="unsized-types.html"><strong aria-hidden="true">3.31.</strong> Unsized Types</a></li><li><a href="operators-and-overloading.html"><strong aria-hidden="true">3.32.</strong> Operators and Overloading</a></li><li><a href="deref-coercions.html"><strong aria-hidden="true">3.33.</strong> Deref coercions</a></li><li><a href="macros.html"><strong aria-hidden="true">3.34.</strong> Macros</a></li><li><a href="raw-pointers.html"><strong aria-hidden="true">3.35.</strong> Raw Pointers</a></li><li><a href="unsafe.html"><strong aria-hidden="true">3.36.</strong> unsafe</a></li></ol></li><li><a href="effective-rust.html"><strong aria-hidden="true">4.</strong> Effective Rust</a></li><li><ol class="section"><li><a href="the-stack-and-the-heap.html"><strong aria-hidden="true">4.1.</strong> The Stack and the Heap</a></li><li><a href="testing.html"><strong aria-hidden="true">4.2.</strong> Testing</a></li><li><a href="conditional-compilation.html"><strong aria-hidden="true">4.3.</strong> Conditional Compilation</a></li><li><a href="documentation.html"><strong aria-hidden="true">4.4.</strong> Documentation</a></li><li><a href="iterators.html"><strong aria-hidden="true">4.5.</strong> Iterators</a></li><li><a href="concurrency.html"><strong aria-hidden="true">4.6.</strong> Concurrency</a></li><li><a href="error-handling.html"><strong aria-hidden="true">4.7.</strong> Error Handling</a></li><li><a href="choosing-your-guarantees.html"><strong aria-hidden="true">4.8.</strong> Choosing your Guarantees</a></li><li><a href="ffi.html"><strong aria-hidden="true">4.9.</strong> FFI</a></li><li><a href="borrow-and-asref.html"><strong aria-hidden="true">4.10.</strong> Borrow and AsRef</a></li><li><a href="release-channels.html"><strong aria-hidden="true">4.11.</strong> Release Channels</a></li><li><a href="using-rust-without-the-standard-library.html"><strong aria-hidden="true">4.12.</strong> Using Rust without the standard library</a></li><li><a href="procedural-macros.html"><strong aria-hidden="true">4.13.</strong> Procedural Macros (and custom derive)</a></li></ol></li><li><a href="glossary.html"><strong aria-hidden="true">5.</strong> Glossary</a></li><li><a href="syntax-index.html" class="active"><strong aria-hidden="true">6.</strong> Syntax Index</a></li><li><a href="bibliography.html"><strong aria-hidden="true">7.</strong> Bibliography</a></li></ol>
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<h1 class="menu-title">The Rust Programming Language</h1>
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<a class="header" href="syntax-index.html#syntax-index" id="syntax-index"><h1>Syntax Index</h1></a>
<a class="header" href="syntax-index.html#keywords" id="keywords"><h2>Keywords</h2></a>
<ul>
<li><code>as</code>: primitive casting, or disambiguating the specific trait containing an item. See <a href="casting-between-types.html#as">Casting Between Types (<code>as</code>)</a>, <a href="ufcs.html#angle-bracket-form">Universal Function Call Syntax (Angle-bracket Form)</a>, <a href="associated-types.html">Associated Types</a>.</li>
<li><code>break</code>: break out of loop. See <a href="loops.html#ending-iteration-early">Loops (Ending Iteration Early)</a>.</li>
<li><code>const</code>: constant items and constant raw pointers. See <a href="const-and-static.html"><code>const</code> and <code>static</code></a>, <a href="raw-pointers.html">Raw Pointers</a>.</li>
<li><code>continue</code>: continue to next loop iteration. See <a href="loops.html#ending-iteration-early">Loops (Ending Iteration Early)</a>.</li>
<li><code>crate</code>: external crate linkage. See <a href="crates-and-modules.html#importing-external-crates">Crates and Modules (Importing External Crates)</a>.</li>
<li><code>else</code>: fallback for <code>if</code> and <code>if let</code> constructs. See <a href="if.html"><code>if</code></a>, <a href="if-let.html"><code>if let</code></a>.</li>
<li><code>enum</code>: defining enumeration. See <a href="enums.html">Enums</a>.</li>
<li><code>extern</code>: external crate, function, and variable linkage. See <a href="crates-and-modules.html#importing-external-crates">Crates and Modules (Importing External Crates)</a>, <a href="ffi.html">Foreign Function Interface</a>.</li>
<li><code>false</code>: boolean false literal. See <a href="primitive-types.html#booleans">Primitive Types (Booleans)</a>.</li>
<li><code>fn</code>: function definition and function pointer types. See <a href="functions.html">Functions</a>.</li>
<li><code>for</code>: iterator loop, part of trait <code>impl</code> syntax, and higher-ranked lifetime syntax. See <a href="loops.html#for">Loops (<code>for</code>)</a>, <a href="method-syntax.html">Method Syntax</a>.</li>
<li><code>if</code>: conditional branching. See <a href="if.html"><code>if</code></a>, <a href="if-let.html"><code>if let</code></a>.</li>
<li><code>impl</code>: inherent and trait implementation blocks. See <a href="method-syntax.html">Method Syntax</a>.</li>
<li><code>in</code>: part of <code>for</code> loop syntax. See <a href="loops.html#for">Loops (<code>for</code>)</a>.</li>
<li><code>let</code>: variable binding. See <a href="variable-bindings.html">Variable Bindings</a>.</li>
<li><code>loop</code>: unconditional, infinite loop. See <a href="loops.html#loop">Loops (<code>loop</code>)</a>.</li>
<li><code>match</code>: pattern matching. See <a href="match.html">Match</a>.</li>
<li><code>mod</code>: module declaration. See <a href="crates-and-modules.html#defining-modules">Crates and Modules (Defining Modules)</a>.</li>
<li><code>move</code>: part of closure syntax. See <a href="closures.html#move-closures">Closures (<code>move</code> closures)</a>.</li>
<li><code>mut</code>: denotes mutability in pointer types and pattern bindings. See <a href="mutability.html">Mutability</a>.</li>
<li><code>pub</code>: denotes public visibility in <code>struct</code> fields, <code>impl</code> blocks, and modules. See <a href="crates-and-modules.html#exporting-a-public-interface">Crates and Modules (Exporting a Public Interface)</a>.</li>
<li><code>ref</code>: by-reference binding. See <a href="patterns.html#ref-and-ref-mut">Patterns (<code>ref</code> and <code>ref mut</code>)</a>.</li>
<li><code>return</code>: return from function. See <a href="functions.html#early-returns">Functions (Early Returns)</a>.</li>
<li><code>Self</code>: implementor type alias. See <a href="traits.html">Traits</a>.</li>
<li><code>self</code>: method subject. See <a href="method-syntax.html#method-calls">Method Syntax (Method Calls)</a>.</li>
<li><code>static</code>: global variable. See <a href="const-and-static.html#static"><code>const</code> and <code>static</code> (<code>static</code>)</a>.</li>
<li><code>struct</code>: structure definition. See <a href="structs.html">Structs</a>.</li>
<li><code>trait</code>: trait definition. See <a href="traits.html">Traits</a>.</li>
<li><code>true</code>: boolean true literal. See <a href="primitive-types.html#booleans">Primitive Types (Booleans)</a>.</li>
<li><code>type</code>: type alias, and associated type definition. See <a href="type-aliases.html"><code>type</code> Aliases</a>, <a href="associated-types.html">Associated Types</a>.</li>
<li><code>unsafe</code>: denotes unsafe code, functions, traits, and implementations. See <a href="unsafe.html">Unsafe</a>.</li>
<li><code>use</code>: import symbols into scope. See <a href="crates-and-modules.html#importing-modules-with-use">Crates and Modules (Importing Modules with <code>use</code>)</a>.</li>
<li><code>where</code>: type constraint clauses. See <a href="traits.html#where-clause">Traits (<code>where</code> clause)</a>.</li>
<li><code>while</code>: conditional loop. See <a href="loops.html#while">Loops (<code>while</code>)</a>.</li>
</ul>
<a class="header" href="syntax-index.html#operators-and-symbols" id="operators-and-symbols"><h2>Operators and Symbols</h2></a>
<ul>
<li><code>!</code> (<code>ident!(…)</code>, <code>ident!{…}</code>, <code>ident![…]</code>): denotes macro expansion. See <a href="macros.html">Macros</a>.</li>
<li><code>!</code> (<code>!expr</code>): bitwise or logical complement. Overloadable (<code>Not</code>).</li>
<li><code>!=</code> (<code>var != expr</code>): nonequality comparison. Overloadable (<code>PartialEq</code>).</li>
<li><code>%</code> (<code>expr % expr</code>): arithmetic remainder. Overloadable (<code>Rem</code>).</li>
<li><code>%=</code> (<code>var %= expr</code>): arithmetic remainder & assignment. Overloadable (<code>RemAssign</code>).</li>
<li><code>&</code> (<code>expr & expr</code>): bitwise and. Overloadable (<code>BitAnd</code>).</li>
<li><code>&</code> (<code>&expr</code>, <code>&mut expr</code>): borrow. See <a href="references-and-borrowing.html">References and Borrowing</a>.</li>
<li><code>&</code> (<code>&type</code>, <code>&mut type</code>, <code>&'a type</code>, <code>&'a mut type</code>): borrowed pointer type. See <a href="references-and-borrowing.html">References and Borrowing</a>.</li>
<li><code>&=</code> (<code>var &= expr</code>): bitwise and & assignment. Overloadable (<code>BitAndAssign</code>).</li>
<li><code>&&</code> (<code>expr && expr</code>): logical and.</li>
<li><code>*</code> (<code>expr * expr</code>): arithmetic multiplication. Overloadable (<code>Mul</code>).</li>
<li><code>*</code> (<code>*expr</code>): dereference.</li>
<li><code>*</code> (<code>*const type</code>, <code>*mut type</code>): raw pointer. See <a href="raw-pointers.html">Raw Pointers</a>.</li>
<li><code>*=</code> (<code>var *= expr</code>): arithmetic multiplication & assignment. Overloadable (<code>MulAssign</code>).</li>
<li><code>+</code> (<code>expr + expr</code>): arithmetic addition. Overloadable (<code>Add</code>).</li>
<li><code>+</code> (<code>trait + trait</code>, <code>'a + trait</code>): compound type constraint. See <a href="traits.html#multiple-trait-bounds">Traits (Multiple Trait Bounds)</a>.</li>
<li><code>+=</code> (<code>var += expr</code>): arithmetic addition & assignment. Overloadable (<code>AddAssign</code>).</li>
<li><code>,</code>: argument and element separator. See <a href="attributes.html">Attributes</a>, <a href="functions.html">Functions</a>, <a href="structs.html">Structs</a>, <a href="generics.html">Generics</a>, <a href="match.html">Match</a>, <a href="closures.html">Closures</a>, <a href="crates-and-modules.html#importing-modules-with-use">Crates and Modules (Importing Modules with <code>use</code>)</a>.</li>
<li><code>-</code> (<code>expr - expr</code>): arithmetic subtraction. Overloadable (<code>Sub</code>).</li>
<li><code>-</code> (<code>- expr</code>): arithmetic negation. Overloadable (<code>Neg</code>).</li>
<li><code>-=</code> (<code>var -= expr</code>): arithmetic subtraction & assignment. Overloadable (<code>SubAssign</code>).</li>
<li><code>-></code> (<code>fn(…) -> type</code>, <code>|…| -> type</code>): function and closure return type. See <a href="functions.html">Functions</a>, <a href="closures.html">Closures</a>.</li>
<li><code>.</code> (<code>expr.ident</code>): member access. See <a href="structs.html">Structs</a>, <a href="method-syntax.html">Method Syntax</a>.</li>
<li><code>..</code> (<code>..</code>, <code>expr..</code>, <code>..expr</code>, <code>expr..expr</code>): right-exclusive range literal.</li>
<li><code>..</code> (<code>..expr</code>): struct literal update syntax. See <a href="structs.html#update-syntax">Structs (Update syntax)</a>.</li>
<li><code>..</code> (<code>variant(x, ..)</code>, <code>struct_type { x, .. }</code>): "and the rest" pattern binding. See <a href="patterns.html#ignoring-bindings">Patterns (Ignoring bindings)</a>.</li>
<li><code>...</code> (<code>...expr</code>, <code>expr...expr</code>) <em>in an expression</em>: inclusive range expression. See <a href="iterators.html">Iterators</a>.</li>
<li><code>...</code> (<code>expr...expr</code>) <em>in a pattern</em>: inclusive range pattern. See <a href="patterns.html#ranges">Patterns (Ranges)</a>.</li>
<li><code>/</code> (<code>expr / expr</code>): arithmetic division. Overloadable (<code>Div</code>).</li>
<li><code>/=</code> (<code>var /= expr</code>): arithmetic division & assignment. Overloadable (<code>DivAssign</code>).</li>
<li><code>:</code> (<code>pat: type</code>, <code>ident: type</code>): constraints. See <a href="variable-bindings.html">Variable Bindings</a>, <a href="functions.html">Functions</a>, <a href="structs.html">Structs</a>, <a href="traits.html">Traits</a>.</li>
<li><code>:</code> (<code>ident: expr</code>): struct field initializer. See <a href="structs.html">Structs</a>.</li>
<li><code>:</code> (<code>'a: loop {…}</code>): loop label. See <a href="loops.html#loop-labels">Loops (Loops Labels)</a>.</li>
<li><code>;</code>: statement and item terminator.</li>
<li><code>;</code> (<code>[…; len]</code>): part of fixed-size array syntax. See <a href="primitive-types.html#arrays">Primitive Types (Arrays)</a>.</li>
<li><code><<</code> (<code>expr << expr</code>): left-shift. Overloadable (<code>Shl</code>).</li>
<li><code><<=</code> (<code>var <<= expr</code>): left-shift & assignment. Overloadable (<code>ShlAssign</code>).</li>
<li><code><</code> (<code>expr < expr</code>): less-than comparison. Overloadable (<code>PartialOrd</code>).</li>
<li><code><=</code> (<code>var <= expr</code>): less-than or equal-to comparison. Overloadable (<code>PartialOrd</code>).</li>
<li><code>=</code> (<code>var = expr</code>, <code>ident = type</code>): assignment/equivalence. See <a href="variable-bindings.html">Variable Bindings</a>, <a href="type-aliases.html"><code>type</code> Aliases</a>, generic parameter defaults.</li>
<li><code>==</code> (<code>var == expr</code>): equality comparison. Overloadable (<code>PartialEq</code>).</li>
<li><code>=></code> (<code>pat => expr</code>): part of match arm syntax. See <a href="match.html">Match</a>.</li>
<li><code>></code> (<code>expr > expr</code>): greater-than comparison. Overloadable (<code>PartialOrd</code>).</li>
<li><code>>=</code> (<code>var >= expr</code>): greater-than or equal-to comparison. Overloadable (<code>PartialOrd</code>).</li>
<li><code>>></code> (<code>expr >> expr</code>): right-shift. Overloadable (<code>Shr</code>).</li>
<li><code>>>=</code> (<code>var >>= expr</code>): right-shift & assignment. Overloadable (<code>ShrAssign</code>).</li>
<li><code>@</code> (<code>ident @ pat</code>): pattern binding. See <a href="patterns.html#bindings">Patterns (Bindings)</a>.</li>
<li><code>^</code> (<code>expr ^ expr</code>): bitwise exclusive or. Overloadable (<code>BitXor</code>).</li>
<li><code>^=</code> (<code>var ^= expr</code>): bitwise exclusive or & assignment. Overloadable (<code>BitXorAssign</code>).</li>
<li><code>|</code> (<code>expr | expr</code>): bitwise or. Overloadable (<code>BitOr</code>).</li>
<li><code>|</code> (<code>pat | pat</code>): pattern alternatives. See <a href="patterns.html#multiple-patterns">Patterns (Multiple patterns)</a>.</li>
<li><code>|</code> (<code>|…| expr</code>): closures. See <a href="closures.html">Closures</a>.</li>
<li><code>|=</code> (<code>var |= expr</code>): bitwise or & assignment. Overloadable (<code>BitOrAssign</code>).</li>
<li><code>||</code> (<code>expr || expr</code>): logical or.</li>
<li><code>_</code>: "ignored" pattern binding (see <a href="patterns.html#ignoring-bindings">Patterns (Ignoring bindings)</a>). Also used to make integer-literals readable (see <a href="../../reference/tokens.html#integer-literals">Reference (Integer literals)</a>).</li>
<li><code>?</code> (<code>expr?</code>): Error propagation. Returns early when <code>Err(_)</code> is encountered, unwraps otherwise. Similar to the <a href="error-handling.html#the-try-macro"><code>try!</code> macro</a>.</li>
</ul>
<a class="header" href="syntax-index.html#other-syntax" id="other-syntax"><h2>Other Syntax</h2></a>
<!-- Various bits of standalone stuff. -->
<ul>
<li><code>'ident</code>: named lifetime or loop label. See <a href="lifetimes.html">Lifetimes</a>, <a href="loops.html#loop-labels">Loops (Loops Labels)</a>.</li>
<li><code>…u8</code>, <code>…i32</code>, <code>…f64</code>, <code>…usize</code>, …: numeric literal of specific type.</li>
<li><code>"…"</code>: string literal. See <a href="strings.html">Strings</a>.</li>
<li><code>r"…"</code>, <code>r#"…"#</code>, <code>r##"…"##</code>, …: raw string literal, escape characters are not processed. See <a href="../../reference/tokens.html#raw-string-literals">Reference (Raw String Literals)</a>.</li>
<li><code>b"…"</code>: byte string literal, constructs a <code>[u8]</code> instead of a string. See <a href="../../reference/tokens.html#byte-and-byte-string-literals">Reference (Byte String Literals)</a>.</li>
<li><code>br"…"</code>, <code>br#"…"#</code>, <code>br##"…"##</code>, …: raw byte string literal, combination of raw and byte string literal. See <a href="../../reference/tokens.html#raw-byte-string-literals">Reference (Raw Byte String Literals)</a>.</li>
<li><code>'…'</code>: character literal. See <a href="primitive-types.html#char">Primitive Types (<code>char</code>)</a>.</li>
<li><code>b'…'</code>: ASCII byte literal.</li>
<li><code>|…| expr</code>: closure. See <a href="closures.html">Closures</a>.</li>
</ul>
<!-- Path-related syntax -->
<ul>
<li><code>ident::ident</code>: path. See <a href="crates-and-modules.html#defining-modules">Crates and Modules (Defining Modules)</a>.</li>
<li><code>::path</code>: path relative to the crate root (<em>i.e.</em> an explicitly absolute path). See <a href="crates-and-modules.html#re-exporting-with-pub-use">Crates and Modules (Re-exporting with <code>pub use</code>)</a>.</li>
<li><code>self::path</code>: path relative to the current module (<em>i.e.</em> an explicitly relative path). See <a href="crates-and-modules.html#re-exporting-with-pub-use">Crates and Modules (Re-exporting with <code>pub use</code>)</a>.</li>
<li><code>super::path</code>: path relative to the parent of the current module. See <a href="crates-and-modules.html#re-exporting-with-pub-use">Crates and Modules (Re-exporting with <code>pub use</code>)</a>.</li>
<li><code>type::ident</code>, <code><type as trait>::ident</code>: associated constants, functions, and types. See <a href="associated-types.html">Associated Types</a>.</li>
<li><code><type>::…</code>: associated item for a type which cannot be directly named (<em>e.g.</em> <code><&T>::…</code>, <code><[T]>::…</code>, <em>etc.</em>). See <a href="associated-types.html">Associated Types</a>.</li>
<li><code>trait::method(…)</code>: disambiguating a method call by naming the trait which defines it. See <a href="ufcs.html">Universal Function Call Syntax</a>.</li>
<li><code>type::method(…)</code>: disambiguating a method call by naming the type for which it's defined. See <a href="ufcs.html">Universal Function Call Syntax</a>.</li>
<li><code><type as trait>::method(…)</code>: disambiguating a method call by naming the trait <em>and</em> type. See <a href="ufcs.html#angle-bracket-form">Universal Function Call Syntax (Angle-bracket Form)</a>.</li>
</ul>
<!-- Generics -->
<ul>
<li><code>path<…></code> (<em>e.g.</em> <code>Vec<u8></code>): specifies parameters to generic type <em>in a type</em>. See <a href="generics.html">Generics</a>.</li>
<li><code>path::<…></code>, <code>method::<…></code> (<em>e.g.</em> <code>"42".parse::<i32>()</code>): specifies parameters to generic type, function, or method <em>in an expression</em>. See <a href="generics.html#resolving-ambiguities">Generics § Resolving ambiguities</a>.</li>
<li><code>fn ident<…> …</code>: define generic function. See <a href="generics.html">Generics</a>.</li>
<li><code>struct ident<…> …</code>: define generic structure. See <a href="generics.html">Generics</a>.</li>
<li><code>enum ident<…> …</code>: define generic enumeration. See <a href="generics.html">Generics</a>.</li>
<li><code>impl<…> …</code>: define generic implementation.</li>
<li><code>for<…> type</code>: higher-ranked lifetime bounds.</li>
<li><code>type<ident=type></code> (<em>e.g.</em> <code>Iterator<Item=T></code>): a generic type where one or more associated types have specific assignments. See <a href="associated-types.html">Associated Types</a>.</li>
</ul>
<!-- Constraints -->
<ul>
<li><code>T: U</code>: generic parameter <code>T</code> constrained to types that implement <code>U</code>. See <a href="traits.html">Traits</a>.</li>
<li><code>T: 'a</code>: generic type <code>T</code> must outlive lifetime <code>'a</code>. When we say that a type 'outlives' the lifetime, we mean that it cannot transitively contain any references with lifetimes shorter than <code>'a</code>.</li>
<li><code>T : 'static</code>: The generic type <code>T</code> contains no borrowed references other than <code>'static</code> ones.</li>
<li><code>'b: 'a</code>: generic lifetime <code>'b</code> must outlive lifetime <code>'a</code>.</li>
<li><code>T: ?Sized</code>: allow generic type parameter to be a dynamically-sized type. See <a href="unsized-types.html#sized">Unsized Types (<code>?Sized</code>)</a>.</li>
<li><code>'a + trait</code>, <code>trait + trait</code>: compound type constraint. See <a href="traits.html#multiple-trait-bounds">Traits (Multiple Trait Bounds)</a>.</li>
</ul>
<!-- Macros and attributes -->
<ul>
<li><code>#[meta]</code>: outer attribute. See <a href="attributes.html">Attributes</a>.</li>
<li><code>#![meta]</code>: inner attribute. See <a href="attributes.html">Attributes</a>.</li>
<li><code>$ident</code>: macro substitution. See <a href="macros.html">Macros</a>.</li>
<li><code>$ident:kind</code>: macro capture. See <a href="macros.html">Macros</a>.</li>
<li><code>$(…)…</code>: macro repetition. See <a href="macros.html">Macros</a>.</li>
</ul>
<!-- Comments -->
<ul>
<li><code>//</code>: line comment. See <a href="comments.html">Comments</a>.</li>
<li><code>//!</code>: inner line doc comment. See <a href="comments.html">Comments</a>.</li>
<li><code>///</code>: outer line doc comment. See <a href="comments.html">Comments</a>.</li>
<li><code>/*…*/</code>: block comment. See <a href="comments.html">Comments</a>.</li>
<li><code>/*!…*/</code>: inner block doc comment. See <a href="comments.html">Comments</a>.</li>
<li><code>/**…*/</code>: outer block doc comment. See <a href="comments.html">Comments</a>.</li>
</ul>
<!-- Special types -->
<ul>
<li><code>!</code>: always empty Never type. See <a href="functions.html#diverging-functions">Diverging Functions</a>.</li>
</ul>
<!-- Various things involving parens and tuples -->
<ul>
<li><code>()</code>: empty tuple (<em>a.k.a.</em> unit), both literal and type.</li>
<li><code>(expr)</code>: parenthesized expression.</li>
<li><code>(expr,)</code>: single-element tuple expression. See <a href="primitive-types.html#tuples">Primitive Types (Tuples)</a>.</li>
<li><code>(type,)</code>: single-element tuple type. See <a href="primitive-types.html#tuples">Primitive Types (Tuples)</a>.</li>
<li><code>(expr, …)</code>: tuple expression. See <a href="primitive-types.html#tuples">Primitive Types (Tuples)</a>.</li>
<li><code>(type, …)</code>: tuple type. See <a href="primitive-types.html#tuples">Primitive Types (Tuples)</a>.</li>
<li><code>expr(expr, …)</code>: function call expression. Also used to initialize tuple <code>struct</code>s and tuple <code>enum</code> variants. See <a href="functions.html">Functions</a>.</li>
<li><code>ident!(…)</code>, <code>ident!{…}</code>, <code>ident![…]</code>: macro invocation. See <a href="macros.html">Macros</a>.</li>
<li><code>expr.0</code>, <code>expr.1</code>, …: tuple indexing. See <a href="primitive-types.html#tuple-indexing">Primitive Types (Tuple Indexing)</a>.</li>
</ul>
<!-- Bracey things -->
<ul>
<li><code>{…}</code>: block expression.</li>
<li><code>Type {…}</code>: <code>struct</code> literal. See <a href="structs.html">Structs</a>.</li>
</ul>
<!-- Brackety things -->
<ul>
<li><code>[…]</code>: array literal. See <a href="primitive-types.html#arrays">Primitive Types (Arrays)</a>.</li>
<li><code>[expr; len]</code>: array literal containing <code>len</code> copies of <code>expr</code>. See <a href="primitive-types.html#arrays">Primitive Types (Arrays)</a>.</li>
<li><code>[type; len]</code>: array type containing <code>len</code> instances of <code>type</code>. See <a href="primitive-types.html#arrays">Primitive Types (Arrays)</a>.</li>
<li><code>expr[expr]</code>: collection indexing. Overloadable (<code>Index</code>, <code>IndexMut</code>).</li>
<li><code>expr[..]</code>, <code>expr[a..]</code>, <code>expr[..b]</code>, <code>expr[a..b]</code>: collection indexing pretending to be collection slicing, using <code>Range</code>, <code>RangeFrom</code>, <code>RangeTo</code>, <code>RangeFull</code> as the "index".</li>
</ul>
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