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<title>tokio::prelude::task::LocalKey - Rust</title>
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<p class='location'>Struct LocalKey</p><div class="sidebar-elems"><div class="block items"><a class="sidebar-title" href="#methods">Methods</a><div class="sidebar-links"><a href="#method.with">with</a></div><a class="sidebar-title" href="#implementations">Trait Implementations</a><div class="sidebar-links"><a href="#impl-Debug">Debug</a></div></div><p class='location'><a href='../../index.html'>tokio</a>::<wbr><a href='../index.html'>prelude</a>::<wbr><a href='index.html'>task</a></p><script>window.sidebarCurrent = {name: 'LocalKey', ty: 'struct', relpath: ''};</script><script defer src="sidebar-items.js"></script></div>
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<h1 class='fqn'><span class='in-band'>Struct <a href='../../index.html'>tokio</a>::<wbr><a href='../index.html'>prelude</a>::<wbr><a href='index.html'>task</a>::<wbr><a class="struct" href=''>LocalKey</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/futures/task_impl/std/data.rs.html#59-66' title='goto source code'>[src]</a></span></h1>
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<pre class='rust struct'>pub struct LocalKey<T> { /* fields omitted */ }</pre><div class='docblock'><p>A key for task-local data stored in a future's task.</p>
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<p>This type is generated by the <code>task_local!</code> macro and performs very
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similarly to the <code>thread_local!</code> macro and <code>std::thread::LocalKey</code> types.
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Data associated with a <code>LocalKey<T></code> is stored inside of a future's task,
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and the data is destroyed when the future is completed and the task is
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destroyed.</p>
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<p>Task-local data can migrate between threads and hence requires a <code>Send</code>
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bound. Additionally, task-local data also requires the <code>'static</code> bound to
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ensure it lives long enough. When a key is accessed for the first time the
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task's data is initialized with the provided initialization expression to
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the macro.</p>
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<h2 id='methods' class='small-section-header'>
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Methods<a href='#methods' class='anchor'></a>
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<h3 id='impl' class='impl'><span class='in-band'><code>impl<T> <a class="struct" href="../../../tokio/prelude/task/struct.LocalKey.html" title="struct tokio::prelude::task::LocalKey">LocalKey</a><T> <span class="where fmt-newline">where<br> T: 'static + <a class="trait" href="https://doc.rust-lang.org/nightly/core/marker/trait.Send.html" title="trait core::marker::Send">Send</a>, </span></code><a href='#impl' class='anchor'></a></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/futures/task_impl/std/data.rs.html#93-131' title='goto source code'>[src]</a></span></h3>
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<div class='impl-items'><h4 id='method.with' class="method"><span id='with.v' class='invisible'><code>pub fn <a href='#method.with' class='fnname'>with</a><F, R>(&'static self, f: F) -> R <span class="where fmt-newline">where<br> F: <a class="trait" href="https://doc.rust-lang.org/nightly/core/ops/function/trait.FnOnce.html" title="trait core::ops::function::FnOnce">FnOnce</a>(<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.reference.html">&</a>T) -> R, </span></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/futures/task_impl/std/data.rs.html#114-130' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Access this task-local key, running the provided closure with a
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reference to the value.</p>
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<p>This function will access this task-local key to retrieve the data
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associated with the current task and this key. If this is the first time
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this key has been accessed on this task, then the key will be
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initialized with the initialization expression provided at the time the
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<code>task_local!</code> macro was called.</p>
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<p>The provided closure will be provided a shared reference to the
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underlying data associated with this task-local-key. The data itself is
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stored inside of the current task.</p>
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<h1 id="panics" class="section-header"><a href="#panics">Panics</a></h1>
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<p>This function can possibly panic for a number of reasons:</p>
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<ul>
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<li>If there is not a current task.</li>
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<li>If the initialization expression is run and it panics</li>
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<li>If the closure provided panics</li>
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</ul>
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Trait Implementations<a href='#implementations' class='anchor'></a>
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<h3 id='impl-Debug' class='impl'><span class='in-band'><code>impl<T> <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html" title="trait core::fmt::Debug">Debug</a> for <a class="struct" href="../../../tokio/prelude/task/struct.LocalKey.html" title="struct tokio::prelude::task::LocalKey">LocalKey</a><T> <span class="where fmt-newline">where<br> T: <a class="trait" href="https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html" title="trait core::fmt::Debug">Debug</a>, </span></code><a href='#impl-Debug' class='anchor'></a></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/futures/task_impl/std/data.rs.html#58' title='goto source code'>[src]</a></span></h3>
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<div class='impl-items'><h4 id='method.fmt' class="method"><span id='fmt.v' class='invisible'><code>fn <a href='https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html#tymethod.fmt' class='fnname'>fmt</a>(&self, __arg_0: &mut <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Formatter.html" title="struct core::fmt::Formatter">Formatter</a>) -> <a class="enum" href="https://doc.rust-lang.org/nightly/core/result/enum.Result.html" title="enum core::result::Result">Result</a><<a class="primitive" href="https://doc.rust-lang.org/nightly/std/primitive.unit.html">()</a>, <a class="struct" href="https://doc.rust-lang.org/nightly/core/fmt/struct.Error.html" title="struct core::fmt::Error">Error</a>></code></span><span class='out-of-band'><div class='ghost'></div><a class='srclink' href='../../../src/futures/task_impl/std/data.rs.html#58' title='goto source code'>[src]</a></span></h4>
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<div class='docblock'><p>Formats the value using the given formatter. <a href="https://doc.rust-lang.org/nightly/core/fmt/trait.Debug.html#tymethod.fmt">Read more</a></p>
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