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<p class='location'>Crate typed_arena</p><div class="sidebar-elems"><div class="block items"><ul><li><a href="#structs">Structs</a></li></ul></div><p class='location'></p><script>window.sidebarCurrent = {name: 'typed_arena', ty: 'mod', relpath: '../'};</script></div>
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<h1 class='fqn'><span class='in-band'>Crate <a class="mod" href=''>typed_arena</a></span><span class='out-of-band'><span id='render-detail'>
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<div class='docblock'><p>The arena, a fast but limited type of allocator.</p>
<p>Arenas are a type of allocator that destroy the objects within,
all at once, once the arena itself is destroyed.
They do not support deallocation of individual objects while the arena itself is still alive.
The benefit of an arena is very fast allocation; just a vector push.</p>
<p>This is an equivalent of the old
<a href="https://doc.rust-lang.org/1.1.0/arena/struct.TypedArena.html"><code>arena::TypedArena</code></a>
type that was once distributed with nightly rustc but has since been
removed.</p>
<p>It is slightly less efficient, but simpler internally and uses much less unsafe code.
It is based on a <code>Vec&lt;Vec&lt;T&gt;&gt;</code> instead of raw pointers and manual drops.</p>
<h2 id="example" class="section-header"><a href="#example">Example</a></h2>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">typed_arena</span>::<span class="ident">Arena</span>;
<span class="kw">struct</span> <span class="ident">Monster</span> {
<span class="ident">level</span>: <span class="ident">u32</span>,
}
<span class="kw">let</span> <span class="ident">monsters</span> <span class="op">=</span> <span class="ident">Arena</span>::<span class="ident">new</span>();
<span class="kw">let</span> <span class="ident">vegeta</span> <span class="op">=</span> <span class="ident">monsters</span>.<span class="ident">alloc</span>(<span class="ident">Monster</span> { <span class="ident">level</span>: <span class="number">9001</span> });
<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">vegeta</span>.<span class="ident">level</span> <span class="op">&gt;</span> <span class="number">9000</span>);</pre>
<h2 id="safe-cycles" class="section-header"><a href="#safe-cycles">Safe Cycles</a></h2>
<p>All allocated objects get the same lifetime, so you can safely create cycles
between them. This can be useful for certain data structures, such as graphs
and trees with parent pointers.</p>
<pre class="rust rust-example-rendered">
<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">Cell</span>;
<span class="kw">use</span> <span class="ident">typed_arena</span>::<span class="ident">Arena</span>;
<span class="kw">struct</span> <span class="ident">CycleParticipant</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;</span> {
<span class="ident">other</span>: <span class="ident">Cell</span><span class="op">&lt;</span><span class="prelude-ty">Option</span><span class="op">&lt;</span><span class="kw-2">&amp;</span><span class="lifetime">&#39;a</span> <span class="ident">CycleParticipant</span><span class="op">&lt;</span><span class="lifetime">&#39;a</span><span class="op">&gt;&gt;</span><span class="op">&gt;</span>,
}
<span class="kw">let</span> <span class="ident">arena</span> <span class="op">=</span> <span class="ident">Arena</span>::<span class="ident">new</span>();
<span class="kw">let</span> <span class="ident">a</span> <span class="op">=</span> <span class="ident">arena</span>.<span class="ident">alloc</span>(<span class="ident">CycleParticipant</span> { <span class="ident">other</span>: <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>) });
<span class="kw">let</span> <span class="ident">b</span> <span class="op">=</span> <span class="ident">arena</span>.<span class="ident">alloc</span>(<span class="ident">CycleParticipant</span> { <span class="ident">other</span>: <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="prelude-val">None</span>) });
<span class="ident">a</span>.<span class="ident">other</span>.<span class="ident">set</span>(<span class="prelude-val">Some</span>(<span class="ident">b</span>));
<span class="ident">b</span>.<span class="ident">other</span>.<span class="ident">set</span>(<span class="prelude-val">Some</span>(<span class="ident">a</span>));</pre>
</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
<table>
<tr class=' module-item'>
<td><a class="struct" href="struct.Arena.html"
title='struct typed_arena::Arena'>Arena</a></td>
<td class='docblock-short'>
<p>An arena of objects of type <code>T</code>.</p>
</td>
</tr></table></section>
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