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<h1 class="title">Macros</h1>
<p><small>There is a new edition of the book and this is an old link.</small></p>
<blockquote>
<p>While functions and types abstract over code, macros abstract at a syntactic level.</p>
</blockquote>
<div class="example-wrap"><pre class="rust rust-example-rendered">
<span class="macro">macro_rules</span><span class="macro">!</span> <span class="ident">five_times</span> {
(<span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>:<span class="ident">expr</span>) <span class="op">=></span> (<span class="number">5</span> <span class="op">*</span> <span class="macro-nonterminal">$</span><span class="macro-nonterminal">x</span>);
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="macro">assert_eq</span><span class="macro">!</span>(<span class="number">25</span>, <span class="macro">five_times</span><span class="macro">!</span>(<span class="number">2</span> <span class="op">+</span> <span class="number">3</span>));
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Amacro_rules!%20five_times%20%7B%0A%20%20%20%20(%24x%3Aexpr)%20%3D%3E%20(5%20*%20%24x)%3B%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20assert_eq!(25%2C%20five_times!(2%20%2B%203))%3B%0A%7D">Run</a></pre></div>
<hr />
<p>Here are the relevant sections in the new and old books:</p>
<ul>
<li><strong><a href="ch19-06-macros.html">In the current edition: Ch 19.06 Macros</a></strong></li>
<li><a href="https://rustbyexample.com/macros.html">Rust By Example: Macros</a></li>
<li><a href="../reference/macros-by-example.html">In the Rust Reference: Ch 3.1 — Macros by Example</a></li>
<li><small><a href="https://doc.rust-lang.org/1.30.0/book/first-edition/macros.html">In the first edition: Ch 3.34 — Macros</a></small></li>
</ul>
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