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<ul class="chapter"><li class="affix"><a href="introduction.html">Introduction</a></li><li><a href="notation.html"><strong>1.</strong> Notation</a></li><li><ul class="section"><li><a href="unicode-productions.html"><strong>1.1.</strong> Unicode productions</a></li><li><a href="string-table-productions.html"><strong>1.2.</strong> String table productions</a></li></ul></li><li><a href="lexical-structure.html"><strong>2.</strong> Lexical structure</a></li><li><ul class="section"><li><a href="input-format.html"><strong>2.1.</strong> Input format</a></li><li><a href="identifiers.html" class="active"><strong>2.2.</strong> Identifiers</a></li><li><a href="comments.html"><strong>2.3.</strong> Comments</a></li><li><a href="whitespace.html"><strong>2.4.</strong> Whitespace</a></li><li><a href="tokens.html"><strong>2.5.</strong> Tokens</a></li><li><a href="paths.html"><strong>2.6.</strong> Paths</a></li></ul></li><li><a href="macros.html"><strong>3.</strong> Macros</a></li><li><ul class="section"><li><a href="macros-by-example.html"><strong>3.1.</strong> Macros By Example</a></li><li><a href="procedural-macros.html"><strong>3.2.</strong> Procedural Macros</a></li></ul></li><li><a href="crates-and-source-files.html"><strong>4.</strong> Crates and source files</a></li><li><a href="items-and-attributes.html"><strong>5.</strong> Items and attributes</a></li><li><ul class="section"><li><a href="items.html"><strong>5.1.</strong> Items</a></li><li><a href="visibility-and-privacy.html"><strong>5.2.</strong> Visibility and Privacy</a></li><li><a href="attributes.html"><strong>5.3.</strong> Attributes</a></li></ul></li><li><a href="statements-and-expressions.html"><strong>6.</strong> Statements and expressions</a></li><li><ul class="section"><li><a href="statements.html"><strong>6.1.</strong> Statements</a></li><li><a href="expressions.html"><strong>6.2.</strong> Expressions</a></li></ul></li><li><a href="type-system.html"><strong>7.</strong> Type system</a></li><li><ul class="section"><li><a href="types.html"><strong>7.1.</strong> Types</a></li><li><a href="subtyping.html"><strong>7.2.</strong> Subtyping</a></li><li><a href="type-coercions.html"><strong>7.3.</strong> Type coercions</a></li></ul></li><li><a href="special-traits.html"><strong>8.</strong> Special traits</a></li><li><ul class="section"><li><a href="the-copy-trait.html"><strong>8.1.</strong> The Copy trait</a></li><li><a href="the-sized-trait.html"><strong>8.2.</strong> The Sized trait</a></li><li><a href="the-drop-trait.html"><strong>8.3.</strong> The Drop trait</a></li><li><a href="the-deref-trait.html"><strong>8.4.</strong> The Deref trait</a></li><li><a href="the-send-trait.html"><strong>8.5.</strong> The Send trait</a></li><li><a href="the-sync-trait.html"><strong>8.6.</strong> The Sync trait</a></li></ul></li><li><a href="memory-model.html"><strong>9.</strong> Memory model</a></li><li><ul class="section"><li><a href="memory-allocation-and-lifetime.html"><strong>9.1.</strong> Memory allocation and lifetime</a></li><li><a href="memory-ownership.html"><strong>9.2.</strong> Memory ownership</a></li><li><a href="variables.html"><strong>9.3.</strong> Variables</a></li></ul></li><li><a href="linkage.html"><strong>10.</strong> Linkage</a></li><li><a href="unsafety.html"><strong>11.</strong> Unsafety</a></li><li><ul class="section"><li><a href="unsafe-functions.html"><strong>11.1.</strong> Unsafe functions</a></li><li><a href="unsafe-blocks.html"><strong>11.2.</strong> Unsafe blocks</a></li><li><a href="behavior-considered-undefined.html"><strong>11.3.</strong> Behavior considered undefined</a></li><li><a href="behavior-not-considered-unsafe.html"><strong>11.4.</strong> Behavior not considered unsafe</a></li></ul></li><li><a href="influences.html">Appendix: Influences</a></li><li class="affix"><a href="undocumented.html">Appendix: As-yet-undocumented Features</a></li></ul>
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<h1 class="menu-title">The Rust Reference</h1>
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<a class="header" href="identifiers.html#identifiers" id="identifiers"><h1>Identifiers</h1></a>
<p>An identifier is any nonempty Unicode<sup class="footnote-reference"><a href="identifiers.html#non_ascii_idents">1</a></sup> string of the following form:</p>
<p>Either</p>
<ul>
<li>The first character has property <a href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i="><code>XID_start</code></a></li>
<li>The remaining characters have property <a href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i="><code>XID_continue</code></a></li>
</ul>
<p>Or</p>
<ul>
<li>The first character is <code>_</code></li>
<li>The identifier is more than one character, <code>_</code> alone is not an identifier</li>
<li>The remaining characters have property <a href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i="><code>XID_continue</code></a></li>
</ul>
<p>that does <em>not</em> occur in the set of <a href="../grammar.html#keywords">keywords</a>.</p>
<blockquote>
<p><strong>Note</strong>: <a href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Start%3A%5D&abb=on&g=&i="><code>XID_start</code></a> and <a href="http://unicode.org/cldr/utility/list-unicodeset.jsp?a=%5B%3AXID_Continue%3A%5D&abb=on&g=&i="><code>XID_continue</code></a> as character properties cover the
character ranges used to form the more familiar C and Java language-family
identifiers.</p>
</blockquote>
<div class="footnote-definition" id="non_ascii_idents"><sup class="footnote-definition-label">1</sup>
<p>Non-ASCII characters in identifiers are currently feature
gated. This is expected to improve soon.</p>
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