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<h1 class="title">Drop</h1>
<p><small>There is a new edition of the book and this is an old link.</small></p>
<blockquote>
<p><code>Drop</code> lets us customize what happens when a value is about to go out of scope.</p>
</blockquote>
<pre class="rust rust-example-rendered">
<span class="kw">struct</span> <span class="ident">CustomSmartPointer</span> {
<span class="ident">data</span>: <span class="ident">String</span>,
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">CustomSmartPointer</span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"Dropping CustomSmartPointer with data `{}`!"</span>, <span class="self">self</span>.<span class="ident">data</span>);
}
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">c</span> <span class="op">=</span> <span class="ident">CustomSmartPointer</span> { <span class="ident">data</span>: <span class="ident">String</span>::<span class="ident">from</span>(<span class="string">"my stuff"</span>) };
<span class="kw">let</span> <span class="ident">d</span> <span class="op">=</span> <span class="ident">CustomSmartPointer</span> { <span class="ident">data</span>: <span class="ident">String</span>::<span class="ident">from</span>(<span class="string">"other stuff"</span>) };
<span class="macro">println</span><span class="macro">!</span>(<span class="string">"CustomSmartPointers created."</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Astruct%20CustomSmartPointer%20%7B%0A%20%20%20%20data%3A%20String%2C%0A%7D%0A%0Aimpl%20Drop%20for%20CustomSmartPointer%20%7B%0A%20%20%20%20fn%20drop(%26mut%20self)%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Dropping%20CustomSmartPointer%20with%20data%20%60%7B%7D%60!%22%2C%20self.data)%3B%0A%20%20%20%20%7D%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20c%20%3D%20CustomSmartPointer%20%7B%20data%3A%20String%3A%3Afrom(%22my%20stuff%22)%20%7D%3B%0A%20%20%20%20let%20d%20%3D%20CustomSmartPointer%20%7B%20data%3A%20String%3A%3Afrom(%22other%20stuff%22)%20%7D%3B%0A%20%20%20%20println!(%22CustomSmartPointers%20created.%22)%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/ch15-03-drop.html">In the second edition: Ch 15.03 — The <code>Drop</code> Trait Runs Code on Cleanup</a></strong></li>
<li><small><a href="first-edition/drop.html">In the first edition: Ch 3.20 — Drop</a></small></li>
</ul>
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