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<title>typed_arena - Rust</title>
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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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[<span class='inner'>−</span>]
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</span><a class='srclink' href='../src/typed_arena/lib.rs.html#1-316' title='goto source code'>[src]</a></span></h1>
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<div class='docblock'><p>The arena, a fast but limited type of allocator.</p>
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<p>Arenas are a type of allocator that destroy the objects within,
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all at once, once the arena itself is destroyed.
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They do not support deallocation of individual objects while the arena itself is still alive.
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The benefit of an arena is very fast allocation; just a vector push.</p>
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<p>This is an equivalent of the old
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<a href="https://doc.rust-lang.org/1.1.0/arena/struct.TypedArena.html"><code>arena::TypedArena</code></a>
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type that was once distributed with nightly rustc but has since been
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removed.</p>
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<p>It is slightly less efficient, but simpler internally and uses much less unsafe code.
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It is based on a <code>Vec<Vec<T>></code> instead of raw pointers and manual drops.</p>
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<h2 id="example" class="section-header"><a href="#example">Example</a></h2>
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<pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">typed_arena</span>::<span class="ident">Arena</span>;
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<span class="kw">struct</span> <span class="ident">Monster</span> {
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<span class="ident">level</span>: <span class="ident">u32</span>,
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}
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<span class="kw">let</span> <span class="ident">monsters</span> <span class="op">=</span> <span class="ident">Arena</span>::<span class="ident">new</span>();
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<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> });
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<span class="macro">assert</span><span class="macro">!</span>(<span class="ident">vegeta</span>.<span class="ident">level</span> <span class="op">></span> <span class="number">9000</span>);</pre>
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<h2 id="safe-cycles" class="section-header"><a href="#safe-cycles">Safe Cycles</a></h2>
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<p>All allocated objects get the same lifetime, so you can safely create cycles
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between them. This can be useful for certain data structures, such as graphs
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and trees with parent pointers.</p>
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<pre class="rust rust-example-rendered">
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<span class="kw">use</span> <span class="ident">std</span>::<span class="ident">cell</span>::<span class="ident">Cell</span>;
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<span class="kw">use</span> <span class="ident">typed_arena</span>::<span class="ident">Arena</span>;
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<span class="kw">struct</span> <span class="ident">CycleParticipant</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">></span> {
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<span class="ident">other</span>: <span class="ident">Cell</span><span class="op"><</span><span class="prelude-ty">Option</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'a</span> <span class="ident">CycleParticipant</span><span class="op"><</span><span class="lifetime">'a</span><span class="op">>></span><span class="op">></span>,
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}
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<span class="kw">let</span> <span class="ident">arena</span> <span class="op">=</span> <span class="ident">Arena</span>::<span class="ident">new</span>();
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<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>) });
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<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>) });
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<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>));
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<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>
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</div><h2 id='structs' class='section-header'><a href="#structs">Structs</a></h2>
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<table>
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<tr class=' module-item'>
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<td><a class="struct" href="struct.Arena.html"
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title='struct typed_arena::Arena'>Arena</a></td>
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<td class='docblock-short'>
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<p>An arena of objects of type <code>T</code>.</p>
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</td>
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