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<h1 class="title">Closures</h1>
<p><small>There is a new edition of the book and this is an old link.</small></p>
<blockquote>
<p>Anonymous functions you can save in a variable or pass as arguments to other functions.</p>
</blockquote>
<pre class="rust rust-example-rendered">
<span class="kw">let</span> <span class="ident">expensive_closure</span> <span class="op">=</span> <span class="op">|</span><span class="ident">num</span><span class="op">|</span> {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"calculating slowly..."</span>);
<span class="ident">thread</span>::<span class="ident">sleep</span>(<span class="ident">Duration</span>::<span class="ident">from_secs</span>(<span class="number">2</span>));
<span class="ident">num</span>
};<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Afn%20main()%20%7B%0Ause%20std%3A%3Athread%3B%0Ause%20std%3A%3Atime%3A%3ADuration%3B%0A%0Alet%20expensive_closure%20%3D%20%7Cnum%7C%20%7B%0A%20%20%20%20println!(%22calculating%20slowly...%22)%3B%0A%20%20%20%20thread%3A%3Asleep(Duration%3A%3Afrom_secs(2))%3B%0A%20%20%20%20num%0A%7D%3B%0Aexpensive_closure(5)%3B%0A%7D">Run</a></pre>
<hr />
<p>Here are the relevant sections in the new and old books:</p>
<ul>
<li><strong><a href="second-edition/ch13-01-closures.html">In the second edition: Ch 13.01 — Closures</a></strong></li>
<li><small><a href="first-edition/closures.html">In the first edition: Ch 3.23 — Closures</a></small></li>
</ul>
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