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<!doctype html><html lang=en dir=ltr class="blog-wrapper blog-post-page plugin-blog plugin-id-default" data-has-hydrated=false><meta charset=UTF-8><meta name=generator content="Docusaurus v3.6.0"><title data-rh=true>Allocations in Rust: Summary | The Old Speice Guy</title><meta data-rh=true name=viewport content="width=device-width,initial-scale=1.0"><meta data-rh=true name=twitter:card content=summary_large_image><meta data-rh=true property=og:url content=https://speice.io/2019/02/summary><meta data-rh=true property=og:locale content=en><meta data-rh=true name=docusaurus_locale content=en><meta data-rh=true name=docusaurus_tag content=default><meta data-rh=true name=docsearch:language content=en><meta data-rh=true name=docsearch:docusaurus_tag content=default><meta data-rh=true property=og:title content="Allocations in Rust: Summary | The Old Speice Guy"><meta data-rh=true name=description content="While there's a lot of interesting detail captured in this series, it's often helpful 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class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/12/allocation-safety>QADAPT - debug_assert! for allocations</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/12/what-small-business-really-means>More "what companies really mean"</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/10/case-study-optimization>A case study in heaptrack</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/09/isomorphic-apps>Isomorphic desktop apps with Rust</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/09/primitives-in-rust-are-weird>Primitives in Rust are weird (and cool)</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/06/dateutil-parser-to-rust>What I learned porting dateutil to Rust</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/05/hello>Hello!</a></ul><div role=group><h4>Captain's Cookbook</h4><ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/01/captains-cookbook-part-1>Project setup</a><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2018/01/captains-cookbook-part-2>Practical usage</a></ul></ul></div></div><div role=group><h3>2016</h3><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/11/pca-audio-compression>PCA audio compression</a></ul><ul class="sidebarItemList_Yudw clean-list"><li class=sidebarItem__DBe><a class=sidebarItemLink_mo7H href=/2016/10/rustic-repodcasting>A Rustic re-podcasting server</a></ul><ul class="sidebarItemList_Yudw 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href=/2015/11/welcome>Welcome, and an algorithm</a></ul></div></nav></aside><main class="col col--7"><article><header><h1 class=title_f1Hy>Allocations in Rust: Summary</h1><div class="container_mt6G margin-vert--md"><time datetime=2019-02-09T12:00:00.000Z>February 9, 2019</time> · <!-- -->2 min read</div><div class="margin-top--md margin-bottom--sm row"><div class="col col--12 authorCol_Hf19"><div class="avatar margin-bottom--sm"><div class="avatar__intro authorDetails_lV9A"><div class=avatar__name><span class=authorName_yefp>Bradlee Speice</span></div><div class=authorSocials_rSDt><a href=https://github.com/bspeice target=_blank rel="noopener noreferrer" class=authorSocialLink_owbf title=GitHub><svg viewBox="0 0 256 250" width=1em height=1em class="authorSocialLink_owbf githubSvg_Uu4N" style=--dark:#000;--light:#fff preserveAspectRatio=xMidYMid><path d="M128.001 0C57.317 0 0 57.307 0 128.001c0 56.554 36.676 104.535 87.535 121.46 6.397 1.185 8.746-2.777 8.746-6.158 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helpful to have a
document that answers some "yes/no" questions. You may not care about what an <code>Iterator</code> looks like
in assembly, you just need to know whether it allocates an object on the heap or not. And while Rust
will prioritize the fastest behavior it can, here are the rules for each memory type:</p>
<p><strong>Global Allocation</strong>:</p>
<ul>
<li><code>const</code> is a fixed value; the compiler is allowed to copy it wherever useful.</li>
<li><code>static</code> is a fixed reference; the compiler will guarantee it is unique.</li>
</ul>
<p><strong>Stack Allocation</strong>:</p>
<ul>
<li>Everything not using a smart pointer will be allocated on the stack.</li>
<li>Structs, enums, iterators, arrays, and closures are all stack allocated.</li>
<li>Cell types (<code>RefCell</code>) behave like smart pointers, but are stack-allocated.</li>
<li>Inlining (<code>#[inline]</code>) will not affect allocation behavior for better or worse.</li>
<li>Types that are marked <code>Copy</code> are guaranteed to have their contents stack-allocated.</li>
</ul>
<p><strong>Heap Allocation</strong>:</p>
<ul>
<li>Smart pointers (<code>Box</code>, <code>Rc</code>, <code>Mutex</code>, etc.) allocate their contents in heap memory.</li>
<li>Collections (<code>HashMap</code>, <code>Vec</code>, <code>String</code>, etc.) allocate their contents in heap memory.</li>
<li>Some smart pointers in the standard library have counterparts in other crates that don't need heap
memory. If possible, use those.</li>
</ul>
<p><img decoding=async loading=lazy alt="Container Sizes in Rust" src=/assets/images/container-size-7fd54cbb2391e3e7310b0424c5f92cc1.svg width=960 height=540 class=img_ev3q></p>
<p>-- <a href="https://docs.google.com/presentation/d/1q-c7UAyrUlM-eZyTo1pd8SZ0qwA_wYxmPZVOQkoDmH4/edit?usp=sharing" target=_blank rel="noopener noreferrer">Raph Levien</a></div></article><nav class="pagination-nav docusaurus-mt-lg" aria-label="Blog post page navigation"><a class="pagination-nav__link pagination-nav__link--prev" href=/2019/02/08/compiler-optimizations><div class=pagination-nav__sublabel>Older post</div><div class=pagination-nav__label>Allocations in Rust: Compiler optimizations</div></a><a class="pagination-nav__link pagination-nav__link--next" href=/2019/05/making-bread><div class=pagination-nav__sublabel>Newer post</div><div class=pagination-nav__label>Making bread</div></a></nav></main></div></div></div><footer class=footer><div class="container container-fluid"><div class="footer__bottom text--center"><div class=footer__copyright>Copyright © 2024 Bradlee Speice</div></div></div></footer></div>
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