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<p class='location'>Trait Drop</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#required-methods">Required Methods</a><div class="sidebar-links"><a href="#tymethod.drop">drop</a></div><a class="sidebar-title" href="#implementors">Implementors</a></div><p class='location'><a href='../index.html'>core</a>::<wbr><a href='index.html'>ops</a></p><script>window.sidebarCurrent = {name: 'Drop', ty: 'trait', relpath: ''};</script><script defer src="sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Trait <a href='../index.html'>core</a>::<wbr><a href='index.html'>ops</a>::<wbr><a class="trait" href=''>Drop</a></span><span class='out-of-band'><span class='since' title='Stable since Rust version 1.0.0'>1.0.0</span><span id='render-detail'>
<a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">
[<span class='inner'>−</span>]
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</span><a class='srclink' href='../../src/core/ops/drop.rs.html#95-117' title='goto source code'>[src]</a></span></h1>
<pre class='rust trait'><div class="docblock attributes">#[lang = "drop"]
</div>pub trait Drop {
fn <a href='#tymethod.drop' class='fnname'>drop</a>(&mut self);
}</pre><div class='docblock'><p>Used to run some code when a value goes out of scope.
This is sometimes called a 'destructor'.</p>
<p>When a value goes out of scope, it will have its <code>drop</code> method called if
its type implements <code>Drop</code>. Then, any fields the value contains will also
be dropped recursively.</p>
<p>Because of this recursive dropping, you do not need to implement this trait
unless your type needs its own destructor logic.</p>
<p>Refer to <a href="../../book/second-edition/ch15-03-drop.html">the chapter on <code>Drop</code> in <em>The Rust Programming Language</em></a>
for some more elaboration.</p>
<h1 id="examples" class="section-header"><a href="#examples">Examples</a></h1><h2 id="implementing-drop" class="section-header"><a href="#implementing-drop">Implementing <code>Drop</code></a></h2>
<p>The <code>drop</code> method is called when <code>_x</code> goes out of scope, and therefore
<code>main</code> prints <code>Dropping!</code>.</p>
<pre class="rust rust-example-rendered">
<span class="kw">struct</span> <span class="ident">HasDrop</span>;
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">HasDrop</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!"</span>);
}
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">_x</span> <span class="op">=</span> <span class="ident">HasDrop</span>;
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Astruct%20HasDrop%3B%0A%0Aimpl%20Drop%20for%20HasDrop%20%7B%0A%20%20%20%20fn%20drop(%26mut%20self)%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Dropping!%22)%3B%0A%20%20%20%20%7D%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20_x%20%3D%20HasDrop%3B%0A%7D%0A">Run</a></pre>
<h2 id="dropping-is-done-recursively" class="section-header"><a href="#dropping-is-done-recursively">Dropping is done recursively</a></h2>
<p>When <code>outer</code> goes out of scope, the <code>drop</code> method will be called first for
<code>Outer</code>, then for <code>Inner</code>. Therefore, <code>main</code> prints <code>Dropping Outer!</code> and
then <code>Dropping Inner!</code>.</p>
<pre class="rust rust-example-rendered">
<span class="kw">struct</span> <span class="ident">Inner</span>;
<span class="kw">struct</span> <span class="ident">Outer</span>(<span class="ident">Inner</span>);
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Inner</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 Inner!"</span>);
}
}
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">Outer</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 Outer!"</span>);
}
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">_x</span> <span class="op">=</span> <span class="ident">Outer</span>(<span class="ident">Inner</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Astruct%20Inner%3B%0Astruct%20Outer(Inner)%3B%0A%0Aimpl%20Drop%20for%20Inner%20%7B%0A%20%20%20%20fn%20drop(%26mut%20self)%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Dropping%20Inner!%22)%3B%0A%20%20%20%20%7D%0A%7D%0A%0Aimpl%20Drop%20for%20Outer%20%7B%0A%20%20%20%20fn%20drop(%26mut%20self)%20%7B%0A%20%20%20%20%20%20%20%20println!(%22Dropping%20Outer!%22)%3B%0A%20%20%20%20%7D%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20_x%20%3D%20Outer(Inner)%3B%0A%7D%0A">Run</a></pre>
<h2 id="variables-are-dropped-in-reverse-order-of-declaration" class="section-header"><a href="#variables-are-dropped-in-reverse-order-of-declaration">Variables are dropped in reverse order of declaration</a></h2>
<p><code>_first</code> is declared first and <code>_second</code> is declared second, so <code>main</code> will
print <code>Declared second!</code> and then <code>Declared first!</code>.</p>
<pre class="rust rust-example-rendered">
<span class="kw">struct</span> <span class="ident">PrintOnDrop</span>(<span class="kw-2">&</span><span class="lifetime">'static</span> <span class="ident">str</span>);
<span class="kw">impl</span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">PrintOnDrop</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">"{}"</span>, <span class="self">self</span>.<span class="number">0</span>);
}
}
<span class="kw">fn</span> <span class="ident">main</span>() {
<span class="kw">let</span> <span class="ident">_first</span> <span class="op">=</span> <span class="ident">PrintOnDrop</span>(<span class="string">"Declared first!"</span>);
<span class="kw">let</span> <span class="ident">_second</span> <span class="op">=</span> <span class="ident">PrintOnDrop</span>(<span class="string">"Declared second!"</span>);
}<a class="test-arrow" target="_blank" href="https://play.rust-lang.org/?code=%23!%5Ballow(unused)%5D%0Astruct%20PrintOnDrop(%26'static%20str)%3B%0A%0Aimpl%20Drop%20for%20PrintOnDrop%20%7B%0A%20%20%20%20fn%20drop(%26mut%20self)%20%7B%0A%20%20%20%20%20%20%20%20println!(%22%7B%7D%22%2C%20self.0)%3B%0A%20%20%20%20%7D%0A%7D%0A%0Afn%20main()%20%7B%0A%20%20%20%20let%20_first%20%3D%20PrintOnDrop(%22Declared%20first!%22)%3B%0A%20%20%20%20let%20_second%20%3D%20PrintOnDrop(%22Declared%20second!%22)%3B%0A%7D%0A">Run</a></pre>
</div>
<h2 id='required-methods' class='small-section-header'>
Required Methods<a href='#required-methods' class='anchor'></a>
</h2>
<div class='methods'>
<h3 id='tymethod.drop' class='method'><span id='drop.v' class='invisible'><code>fn <a href='#tymethod.drop' class='fnname'>drop</a>(&mut self)</code></span></h3><div class='docblock'><p>Executes the destructor for this type.</p>
<p>This method is called implilcitly when the value goes out of scope,
and cannot be called explicitly (this is compiler error <a href="../../error-index.html#E0040">E0040</a>).
However, the <a href="../../std/mem/fn.drop.html"><code>std::mem::drop</code></a> function in the prelude can be
used to call the argument's <code>Drop</code> implementation.</p>
<p>When this method has been called, <code>self</code> has not yet been deallocated.
That only happens after the method is over.
If this wasn't the case, <code>self</code> would be a dangling reference.</p>
<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
<p>Given that a <a href="../macro.panic.html"><code>panic!</code></a> will call <code>drop</code> as it unwinds, any <a href="../macro.panic.html"><code>panic!</code></a>
in a <code>drop</code> implementation will likely abort.</p>
</div></div>
<h2 id='implementors' class='small-section-header'>
Implementors<a href='#implementors' class='anchor'></a>
</h2>
<ul class='item-list' id='implementors-list'>
</ul><script type="text/javascript" async
src="../../implementors/core/ops/trait.Drop.js">
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