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<ol class="chapter"><li class="affix"><a href="introduction.html">Introduction</a></li><li><a href="notation.html"><strong aria-hidden="true">1.</strong> Notation</a></li><li><a href="lexical-structure.html"><strong aria-hidden="true">2.</strong> Lexical structure</a></li><li><ol class="section"><li><a href="input-format.html"><strong aria-hidden="true">2.1.</strong> Input format</a></li><li><a href="keywords.html"><strong aria-hidden="true">2.2.</strong> Keywords</a></li><li><a href="identifiers.html"><strong aria-hidden="true">2.3.</strong> Identifiers</a></li><li><a href="comments.html" class="active"><strong aria-hidden="true">2.4.</strong> Comments</a></li><li><a href="whitespace.html"><strong aria-hidden="true">2.5.</strong> Whitespace</a></li><li><a href="tokens.html"><strong aria-hidden="true">2.6.</strong> Tokens</a></li><li><a href="paths.html"><strong aria-hidden="true">2.7.</strong> Paths</a></li></ol></li><li><a href="macros.html"><strong aria-hidden="true">3.</strong> Macros</a></li><li><ol class="section"><li><a href="macros-by-example.html"><strong aria-hidden="true">3.1.</strong> Macros By Example</a></li><li><a href="procedural-macros.html"><strong aria-hidden="true">3.2.</strong> Procedural Macros</a></li></ol></li><li><a href="crates-and-source-files.html"><strong aria-hidden="true">4.</strong> Crates and source files</a></li><li><a href="items-and-attributes.html"><strong aria-hidden="true">5.</strong> Items and attributes</a></li><li><ol class="section"><li><a href="items.html"><strong aria-hidden="true">5.1.</strong> Items</a></li><li><ol class="section"><li><a href="items/modules.html"><strong aria-hidden="true">5.1.1.</strong> Modules</a></li><li><a href="items/extern-crates.html"><strong aria-hidden="true">5.1.2.</strong> Extern crates</a></li><li><a href="items/use-declarations.html"><strong aria-hidden="true">5.1.3.</strong> Use declarations</a></li><li><a href="items/functions.html"><strong aria-hidden="true">5.1.4.</strong> Functions</a></li><li><a href="items/type-aliases.html"><strong aria-hidden="true">5.1.5.</strong> Type aliases</a></li><li><a href="items/structs.html"><strong aria-hidden="true">5.1.6.</strong> Structs</a></li><li><a href="items/enumerations.html"><strong aria-hidden="true">5.1.7.</strong> Enumerations</a></li><li><a href="items/unions.html"><strong aria-hidden="true">5.1.8.</strong> Unions</a></li><li><a href="items/constant-items.html"><strong aria-hidden="true">5.1.9.</strong> Constant items</a></li><li><a href="items/static-items.html"><strong aria-hidden="true">5.1.10.</strong> Static items</a></li><li><a href="items/traits.html"><strong aria-hidden="true">5.1.11.</strong> Traits</a></li><li><a href="items/implementations.html"><strong aria-hidden="true">5.1.12.</strong> Implementations</a></li><li><a href="items/external-blocks.html"><strong aria-hidden="true">5.1.13.</strong> External blocks</a></li></ol></li><li><a href="items/generics.html"><strong aria-hidden="true">5.2.</strong> Type and lifetime parameters</a></li><li><a href="items/associated-items.html"><strong aria-hidden="true">5.3.</strong> Associated Items</a></li><li><a href="visibility-and-privacy.html"><strong aria-hidden="true">5.4.</strong> Visibility and Privacy</a></li><li><a href="attributes.html"><strong aria-hidden="true">5.5.</strong> Attributes</a></li></ol></li><li><a href="statements-and-expressions.html"><strong aria-hidden="true">6.</strong> Statements and expressions</a></li><li><ol class="section"><li><a href="statements.html"><strong aria-hidden="true">6.1.</strong> Statements</a></li><li><a href="expressions.html"><strong aria-hidden="true">6.2.</strong> Expressions</a></li><li><ol class="section"><li><a href="expressions/literal-expr.html"><strong aria-hidden="true">6.2.1.</strong> Literal expressions</a></li><li><a href="expressions/path-expr.html"><strong aria-hidden="true">6.2.2.</strong> Path expressions</a></li><li><a href="expressions/block-expr.html"><strong aria-hidden="true">6.2.3.</strong> Block expressions</a></li><li><a href="expressions/operator-expr.html"><strong aria-hidden="true">6.2.4.</strong> Operator expressions</a></li><li><a href="expressions/grouped-expr.html"><strong aria-hidden="true">6.2.5.</strong> Grouped expressions</a></li><li><a href="expressions/array-expr.html"><strong aria-hidden="true">6.2.6.</strong> Array and index expressions</a></li><li><a href="expressions/tuple-expr.html"><strong aria-hidden="true">6.2.7.</strong> Tuple and index expressions</a></li><li><a href="expressions/struct-expr.html"><strong aria-hidden="true">6.2.8.</strong> Struct expressions</a></li><li><a href="expressions/enum-variant-expr.html"><strong aria-hidden="true">6.2.9.</strong> Enum variant expressions</a></li><li><a href="expressions/call-expr.html"><strong aria-hidden="true">6.2.10.</strong> Call expressions</a></li><li><a href="expressions/method-call-expr.html"><strong aria-hidden="true">6.2.11.</strong> Method call expressions</a></li><li><a href="expressions/field-expr.html"><strong aria-hidden="true">6.2.12.</strong> Field access expressions</a></li><li><a href="expressions/closure-expr.html"><strong aria-hidden="true">6.2.13.</strong> Closure expressions</a></li><li><a href="expressions/loop-expr.html"><strong aria-hidden="true">6.2.14.</strong> Loop expressions</a></li><li><a href="expressions/range-expr.html"><strong aria-hidden="true">6.2.15.</strong> Range expressions</a></li><li><a href="expressions/if-expr.html"><strong aria-hidden="true">6.2.16.</strong> If and if let expressions</a></li><li><a href="expressions/match-expr.html"><strong aria-hidden="true">6.2.17.</strong> Match expressions</a></li><li><a href="expressions/return-expr.html"><strong aria-hidden="true">6.2.18.</strong> Return expressions</a></li></ol></li></ol></li><li><a href="type-system.html"><strong aria-hidden="true">7.</strong> Type system</a></li><li><ol class="section"><li><a href="types.html"><strong aria-hidden="true">7.1.</strong> Types</a></li><li><a href="dynamically-sized-types.html"><strong aria-hidden="true">7.2.</strong> Dynamically Sized Types</a></li><li><a href="type-layout.html"><strong aria-hidden="true">7.3.</strong> Type layout</a></li><li><a href="interior-mutability.html"><strong aria-hidden="true">7.4.</strong> Interior mutability</a></li><li><a href="subtyping.html"><strong aria-hidden="true">7.5.</strong> Subtyping and Variance</a></li><li><a href="trait-bounds.html"><strong aria-hidden="true">7.6.</strong> Trait and lifetime bounds</a></li><li><a href="type-coercions.html"><strong aria-hidden="true">7.7.</strong> Type coercions</a></li><li><a href="destructors.html"><strong aria-hidden="true">7.8.</strong> Destructors</a></li><li><a href="lifetime-elision.html"><strong aria-hidden="true">7.9.</strong> Lifetime elision</a></li></ol></li><li><a href="special-types-and-traits.html"><strong aria-hidden="true">8.</strong> Special types and traits</a></li><li><a href="memory-model.html"><strong aria-hidden="true">9.</strong> Memory model</a></li><li><ol class="section"><li><a href="memory-allocation-and-lifetime.html"><strong aria-hidden="true">9.1.</strong> Memory allocation and lifetime</a></li><li><a href="memory-ownership.html"><strong aria-hidden="true">9.2.</strong> Memory ownership</a></li><li><a href="variables.html"><strong aria-hidden="true">9.3.</strong> Variables</a></li></ol></li><li><a href="linkage.html"><strong aria-hidden="true">10.</strong> Linkage</a></li><li><a href="unsafety.html"><strong aria-hidden="true">11.</strong> Unsafety</a></li><li><ol class="section"><li><a href="unsafe-functions.html"><strong aria-hidden="true">11.1.</strong> Unsafe functions</a></li><li><a href="unsafe-blocks.html"><strong aria-hidden="true">11.2.</strong> Unsafe blocks</a></li><li><a href="behavior-considered-undefined.html"><strong aria-hidden="true">11.3.</strong> Behavior considered undefined</a></li><li><a href="behavior-not-considered-unsafe.html"><strong aria-hidden="true">11.4.</strong> Behavior not considered unsafe</a></li></ol></li><li><a href="influences.html">Appendix: Influences</a></li><li class="affix"><a href="undocumented.html">Appendix: As-yet-undocumented Features</a></li><li class="affix"><a href="glossary.html">Appendix: Glossary</a></li></ol>
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For now, this reference is a best-effort document. We strive for validity
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teams will work together to figure out how best to do this. Until then, this
is a best-effort attempt. If you find something wrong or missing, file an
<a href="https://github.com/rust-lang-nursery/reference/issues">issue</a> or
send in a pull request.
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<a class="header" href="comments.html#comments" id="comments"><h1>Comments</h1></a>
<blockquote>
<p><strong><sup>Lexer</sup></strong><br />
LINE_COMMENT :<br />
<code>//</code> (~[<code>/</code> <code>!</code>] | <code>//</code>) ~<code>\n</code><sup>*</sup><br />
| <code>//</code></p>
<p>BLOCK_COMMENT :<br />
<code>/*</code> (~[<code>*</code> <code>!</code>] | <code>**</code> | <em>BlockCommentOrDoc</em>)
(<em>BlockCommentOrDoc</em> | ~<code>*/</code>)<sup>*</sup> <code>*/</code><br />
| <code>/**/</code><br />
| <code>/***/</code></p>
<p>INNER_LINE_DOC :<br />
<code>//!</code> ~[<code>\n</code> <em>IsolatedCR</em>]<sup>*</sup></p>
<p>INNER_BLOCK_DOC :<br />
<code>/*!</code> ( <em>BlockCommentOrDoc</em> | ~[<code>*/</code> <em>IsolatedCR</em>] )<sup>*</sup> <code>*/</code></p>
<p>OUTER_LINE_DOC :<br />
<code>///</code> (~<code>/</code> ~[<code>\n</code> <em>IsolatedCR</em>]<sup>*</sup>)<sup>?</sup></p>
<p>OUTER_BLOCK_DOC :<br />
<code>/**</code> (~<code>*</code> | <em>BlockCommentOrDoc</em> )
(<em>BlockCommentOrDoc</em> | ~[<code>*/</code> <em>IsolatedCR</em>])<sup>*</sup> <code>*/</code></p>
<p><em>BlockCommentOrDoc</em> :<br />
BLOCK_COMMENT<br />
| OUTER_BLOCK_DOC<br />
| INNER_BLOCK_DOC</p>
<p><em>IsolatedCR</em> :<br />
<em>A <code>\r</code> not followed by a <code>\n</code></em></p>
</blockquote>
<a class="header" href="comments.html#non-doc-comments" id="non-doc-comments"><h2>Non-doc comments</h2></a>
<p>Comments in Rust code follow the general C++ style of line (<code>//</code>) and
block (<code>/* ... */</code>) comment forms. Nested block comments are supported.</p>
<p>Non-doc comments are interpreted as a form of whitespace.</p>
<a class="header" href="comments.html#doc-comments" id="doc-comments"><h2>Doc comments</h2></a>
<p>Line doc comments beginning with exactly <em>three</em> slashes (<code>///</code>), and block
doc comments (<code>/** ... */</code>), both inner doc comments, are interpreted as a
special syntax for <code>doc</code> <a href="attributes.html">attributes</a>. That is, they are equivalent to writing
<code>#[doc="..."]</code> around the body of the comment, i.e., <code>/// Foo</code> turns into
<code>#[doc="Foo"]</code> and <code>/** Bar */</code> turns into <code>#[doc="Bar"]</code>.</p>
<p>Line comments beginning with <code>//!</code> and block comments <code>/*! ... */</code> are
doc comments that apply to the parent of the comment, rather than the item
that follows. That is, they are equivalent to writing <code>#![doc="..."]</code> around
the body of the comment. <code>//!</code> comments are usually used to document
modules that occupy a source file.</p>
<p>Isolated CRs (<code>\r</code>), i.e. not followed by LF (<code>\n</code>), are not allowed in doc
comments.</p>
<a class="header" href="comments.html#examples" id="examples"><h2>Examples</h2></a>
<pre><pre class="playpen"><code class="language-rust">
# #![allow(unused_variables)]
#fn main() {
//! A doc comment that applies to the implicit anonymous module of this crate
pub mod outer_module {
//! - Inner line doc
//!! - Still an inner line doc (but with a bang at the beginning)
/*! - Inner block doc */
/*!! - Still an inner block doc (but with a bang at the beginning) */
// - Only a comment
/// - Outer line doc (exactly 3 slashes)
//// - Only a comment
/* - Only a comment */
/** - Outer block doc (exactly) 2 asterisks */
/*** - Only a comment */
pub mod inner_module {}
pub mod nested_comments {
/* In Rust /* we can /* nest comments */ */ */
// All three types of block comments can contain or be nested inside
// any other type:
/* /* */ /** */ /*! */ */
/*! /* */ /** */ /*! */ */
/** /* */ /** */ /*! */ */
pub mod dummy_item {}
}
pub mod degenerate_cases {
// empty inner line doc
//!
// empty inner block doc
/*!*/
// empty line comment
//
// empty outer line doc
///
// empty block comment
/**/
pub mod dummy_item {}
// empty 2-asterisk block isn't a doc block, it is a block comment
/***/
}
/* The next one isn't allowed because outer doc comments
require an item that will receive the doc */
/// Where is my item?
# mod boo {}
}
#}</code></pre></pre>
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