| <!DOCTYPE html><html lang="en"><head><meta charset="utf-8"><meta name="viewport" content="width=device-width, initial-scale=1.0"><meta name="generator" content="rustdoc"><meta name="description" content="A thread-safe cell which can be written to only once."><meta name="keywords" content="rust, rustlang, rust-lang, OnceCell"><title>OnceCell in once_cell::sync - Rust</title><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Regular.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../FiraSans-Medium.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Regular.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceSerif4-Bold.ttf.woff2"><link rel="preload" as="font" type="font/woff2" crossorigin href="../../SourceCodePro-Semibold.ttf.woff2"><link 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href="../../once_cell/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2></h2></nav><nav class="sidebar"><a class="sidebar-logo" href="../../once_cell/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">OnceCell</a></h2><div class="sidebar-elems"><section><h3><a href="#implementations">Methods</a></h3><ul class="block"><li><a href="#method.get">get</a></li><li><a href="#method.get_mut">get_mut</a></li><li><a href="#method.get_or_init">get_or_init</a></li><li><a href="#method.get_or_try_init">get_or_try_init</a></li><li><a href="#method.get_unchecked">get_unchecked</a></li><li><a href="#method.into_inner">into_inner</a></li><li><a href="#method.new">new</a></li><li><a href="#method.set">set</a></li><li><a href="#method.take">take</a></li><li><a href="#method.try_insert">try_insert</a></li><li><a href="#method.wait">wait</a></li><li><a href="#method.with_value">with_value</a></li></ul><h3><a href="#trait-implementations">Trait Implementations</a></h3><ul class="block"><li><a href="#impl-Clone-for-OnceCell%3CT%3E">Clone</a></li><li><a href="#impl-Debug-for-OnceCell%3CT%3E">Debug</a></li><li><a href="#impl-Default-for-OnceCell%3CT%3E">Default</a></li><li><a href="#impl-Eq-for-OnceCell%3CT%3E">Eq</a></li><li><a href="#impl-From%3CT%3E-for-OnceCell%3CT%3E">From<T></a></li><li><a href="#impl-PartialEq%3COnceCell%3CT%3E%3E-for-OnceCell%3CT%3E">PartialEq<OnceCell<T>></a></li></ul><h3><a href="#synthetic-implementations">Auto Trait Implementations</a></h3><ul class="block"><li><a href="#impl-RefUnwindSafe-for-OnceCell%3CT%3E">RefUnwindSafe</a></li><li><a href="#impl-Send-for-OnceCell%3CT%3E">Send</a></li><li><a href="#impl-Sync-for-OnceCell%3CT%3E">Sync</a></li><li><a href="#impl-Unpin-for-OnceCell%3CT%3E">Unpin</a></li><li><a href="#impl-UnwindSafe-for-OnceCell%3CT%3E">UnwindSafe</a></li></ul><h3><a href="#blanket-implementations">Blanket Implementations</a></h3><ul class="block"><li><a href="#impl-Any-for-OnceCell%3CT%3E">Any</a></li><li><a href="#impl-Borrow%3CT%3E-for-OnceCell%3CT%3E">Borrow<T></a></li><li><a href="#impl-BorrowMut%3CT%3E-for-OnceCell%3CT%3E">BorrowMut<T></a></li><li><a href="#impl-From%3C!%3E-for-OnceCell%3CT%3E">From<!></a></li><li><a href="#impl-From%3CT%3E-for-OnceCell%3CT%3E-1">From<T></a></li><li><a href="#impl-Into%3CU%3E-for-OnceCell%3CT%3E">Into<U></a></li><li><a href="#impl-ToOwned-for-OnceCell%3CT%3E">ToOwned</a></li><li><a href="#impl-TryFrom%3CU%3E-for-OnceCell%3CT%3E">TryFrom<U></a></li><li><a href="#impl-TryInto%3CU%3E-for-OnceCell%3CT%3E">TryInto<U></a></li></ul></section><h2><a href="index.html">In once_cell::sync</a></h2></div></nav><main><div class="width-limiter"><nav class="sub"><form class="search-form"><div class="search-container"><span></span><input class="search-input" name="search" autocomplete="off" spellcheck="false" placeholder="Click or press ‘S’ to search, ‘?’ for more options…" type="search"><div id="help-button" title="help" tabindex="-1"><a href="../../help.html">?</a></div><div id="settings-menu" tabindex="-1"><a href="../../settings.html" title="settings"><img width="22" height="22" alt="Change settings" src="../../wheel.svg"></a></div></div></form></nav><section id="main-content" class="content"><div class="main-heading"><h1 class="fqn">Struct <a href="../index.html">once_cell</a>::<wbr><a href="index.html">sync</a>::<wbr><a class="struct" href="#">OnceCell</a><button id="copy-path" onclick="copy_path(this)" title="Copy item path to clipboard"><img src="../../clipboard.svg" width="19" height="18" alt="Copy item path"></button></h1><span class="out-of-band"><a class="srclink" href="../../src/once_cell/lib.rs.html#903">source</a> · <a id="toggle-all-docs" href="javascript:void(0)" title="collapse all docs">[<span class="inner">−</span>]</a></span></div><div class="item-decl"><pre class="rust struct"><code>pub struct OnceCell<T>(_);</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A thread-safe cell which can be written to only once.</p> |
| <p><code>OnceCell</code> provides <code>&</code> references to the contents without RAII guards.</p> |
| <p>Reading a non-<code>None</code> value out of <code>OnceCell</code> establishes a |
| happens-before relationship with a corresponding write. For example, if |
| thread A initializes the cell with <code>get_or_init(f)</code>, and thread B |
| subsequently reads the result of this call, B also observes all the side |
| effects of <code>f</code>.</p> |
| <h2 id="example"><a href="#example">Example</a></h2> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">static </span>CELL: OnceCell<String> = OnceCell::new(); |
| <span class="macro">assert!</span>(CELL.get().is_none()); |
| |
| std::thread::spawn(|| { |
| <span class="kw">let </span>value: <span class="kw-2">&</span>String = CELL.get_or_init(|| { |
| <span class="string">"Hello, World!"</span>.to_string() |
| }); |
| <span class="macro">assert_eq!</span>(value, <span class="string">"Hello, World!"</span>); |
| }).join().unwrap(); |
| |
| <span class="kw">let </span>value: <span class="prelude-ty">Option</span><<span class="kw-2">&</span>String> = CELL.get(); |
| <span class="macro">assert!</span>(value.is_some()); |
| <span class="macro">assert_eq!</span>(value.unwrap().as_str(), <span class="string">"Hello, World!"</span>);</code></pre></div> |
| </div></details><h2 id="implementations" class="small-section-header">Implementations<a href="#implementations" class="anchor"></a></h2><div id="implementations-list"><details class="rustdoc-toggle implementors-toggle" open><summary><section id="impl-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#950-1222">source</a><a href="#impl-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.new" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#952-954">source</a><h4 class="code-header">pub const fn <a href="#method.new" class="fnname">new</a>() -> <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h4></section></summary><div class="docblock"><p>Creates a new empty cell.</p> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.with_value" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#957-959">source</a><h4 class="code-header">pub const fn <a href="#method.with_value" class="fnname">with_value</a>(value: T) -> <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h4></section></summary><div class="docblock"><p>Creates a new initialized cell.</p> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.get" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#965-972">source</a><h4 class="code-header">pub fn <a href="#method.get" class="fnname">get</a>(&self) -> Option<&T></h4></section></summary><div class="docblock"><p>Gets the reference to the underlying value.</p> |
| <p>Returns <code>None</code> if the cell is empty, or being initialized. This |
| method never blocks.</p> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.wait" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#995-1003">source</a><h4 class="code-header">pub fn <a href="#method.wait" class="fnname">wait</a>(&self) -> &T</h4></section></summary><div class="docblock"><p>Gets the reference to the underlying value, blocking the current |
| thread until it is set.</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>cell = std::sync::Arc::new(OnceCell::new()); |
| <span class="kw">let </span>t = std::thread::spawn({ |
| <span class="kw">let </span>cell = std::sync::Arc::clone(<span class="kw-2">&</span>cell); |
| <span class="kw">move </span>|| cell.set(<span class="number">92</span>).unwrap() |
| }); |
| |
| <span class="comment">// Returns immediately, but might return None. |
| </span><span class="kw">let </span>_value_or_none = cell.get(); |
| |
| <span class="comment">// Will return 92, but might block until the other thread does `.set`. |
| </span><span class="kw">let </span>value: <span class="kw-2">&</span>u32 = cell.wait(); |
| <span class="macro">assert_eq!</span>(<span class="kw-2">*</span>value, <span class="number">92</span>); |
| t.join().unwrap();</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.get_mut" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1021-1023">source</a><h4 class="code-header">pub fn <a href="#method.get_mut" class="fnname">get_mut</a>(&mut self) -> Option<&mut T></h4></section></summary><div class="docblock"><p>Gets the mutable reference to the underlying value.</p> |
| <p>Returns <code>None</code> if the cell is empty.</p> |
| <p>This method is allowed to violate the invariant of writing to a <code>OnceCell</code> |
| at most once because it requires <code>&mut</code> access to <code>self</code>. As with all |
| interior mutability, <code>&mut</code> access permits arbitrary modification:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>cell: OnceCell<u32> = OnceCell::new(); |
| cell.set(<span class="number">92</span>).unwrap(); |
| cell = OnceCell::new();</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.get_unchecked" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1033-1035">source</a><h4 class="code-header">pub unsafe fn <a href="#method.get_unchecked" class="fnname">get_unchecked</a>(&self) -> &T</h4></section></summary><div class="docblock"><p>Get the reference to the underlying value, without checking if the |
| cell is initialized.</p> |
| <h5 id="safety"><a href="#safety">Safety</a></h5> |
| <p>Caller must ensure that the cell is in initialized state, and that |
| the contents are acquired by (synchronized to) this thread.</p> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.set" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1060-1065">source</a><h4 class="code-header">pub fn <a href="#method.set" class="fnname">set</a>(&self, value: T) -> Result<(), T></h4></section></summary><div class="docblock"><p>Sets the contents of this cell to <code>value</code>.</p> |
| <p>Returns <code>Ok(())</code> if the cell was empty and <code>Err(value)</code> if it was |
| full.</p> |
| <h5 id="example-1"><a href="#example-1">Example</a></h5> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">static </span>CELL: OnceCell<i32> = OnceCell::new(); |
| |
| <span class="kw">fn </span>main() { |
| <span class="macro">assert!</span>(CELL.get().is_none()); |
| |
| std::thread::spawn(|| { |
| <span class="macro">assert_eq!</span>(CELL.set(<span class="number">92</span>), <span class="prelude-val">Ok</span>(())); |
| }).join().unwrap(); |
| |
| <span class="macro">assert_eq!</span>(CELL.set(<span class="number">62</span>), <span class="prelude-val">Err</span>(<span class="number">62</span>)); |
| <span class="macro">assert_eq!</span>(CELL.get(), <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="number">92</span>)); |
| }</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.try_insert" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1082-1089">source</a><h4 class="code-header">pub fn <a href="#method.try_insert" class="fnname">try_insert</a>(&self, value: T) -> Result<&T, (&T, T)></h4></section></summary><div class="docblock"><p>Like <a href="struct.OnceCell.html#method.set"><code>set</code></a>, but also returns a reference to the final cell value.</p> |
| <h5 id="example-2"><a href="#example-2">Example</a></h5> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::unsync::OnceCell; |
| |
| <span class="kw">let </span>cell = OnceCell::new(); |
| <span class="macro">assert!</span>(cell.get().is_none()); |
| |
| <span class="macro">assert_eq!</span>(cell.try_insert(<span class="number">92</span>), <span class="prelude-val">Ok</span>(<span class="kw-2">&</span><span class="number">92</span>)); |
| <span class="macro">assert_eq!</span>(cell.try_insert(<span class="number">62</span>), <span class="prelude-val">Err</span>((<span class="kw-2">&</span><span class="number">92</span>, <span class="number">62</span>))); |
| |
| <span class="macro">assert!</span>(cell.get().is_some());</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.get_or_init" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1117-1126">source</a><h4 class="code-header">pub fn <a href="#method.get_or_init" class="fnname">get_or_init</a><F>(&self, f: F) -> &T<span class="where fmt-newline">where<br> F: FnOnce() -> T,</span></h4></section></summary><div class="docblock"><p>Gets the contents of the cell, initializing it with <code>f</code> if the cell |
| was empty.</p> |
| <p>Many threads may call <code>get_or_init</code> concurrently with different |
| initializing functions, but it is guaranteed that only one function |
| will be executed.</p> |
| <h5 id="panics"><a href="#panics">Panics</a></h5> |
| <p>If <code>f</code> panics, the panic is propagated to the caller, and the cell |
| remains uninitialized.</p> |
| <p>It is an error to reentrantly initialize the cell from <code>f</code>. The |
| exact outcome is unspecified. Current implementation deadlocks, but |
| this may be changed to a panic in the future.</p> |
| <h5 id="example-3"><a href="#example-3">Example</a></h5> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span>cell = OnceCell::new(); |
| <span class="kw">let </span>value = cell.get_or_init(|| <span class="number">92</span>); |
| <span class="macro">assert_eq!</span>(value, <span class="kw-2">&</span><span class="number">92</span>); |
| <span class="kw">let </span>value = cell.get_or_init(|| <span class="macro">unreachable!</span>()); |
| <span class="macro">assert_eq!</span>(value, <span class="kw-2">&</span><span class="number">92</span>);</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.get_or_try_init" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1154-1168">source</a><h4 class="code-header">pub fn <a href="#method.get_or_try_init" class="fnname">get_or_try_init</a><F, E>(&self, f: F) -> Result<&T, E><span class="where fmt-newline">where<br> F: FnOnce() -> Result<T, E>,</span></h4></section></summary><div class="docblock"><p>Gets the contents of the cell, initializing it with <code>f</code> if |
| the cell was empty. If the cell was empty and <code>f</code> failed, an |
| error is returned.</p> |
| <h5 id="panics-1"><a href="#panics-1">Panics</a></h5> |
| <p>If <code>f</code> panics, the panic is propagated to the caller, and |
| the cell remains uninitialized.</p> |
| <p>It is an error to reentrantly initialize the cell from <code>f</code>. |
| The exact outcome is unspecified. Current implementation |
| deadlocks, but this may be changed to a panic in the future.</p> |
| <h5 id="example-4"><a href="#example-4">Example</a></h5> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span>cell = OnceCell::new(); |
| <span class="macro">assert_eq!</span>(cell.get_or_try_init(|| <span class="prelude-val">Err</span>(())), <span class="prelude-val">Err</span>(())); |
| <span class="macro">assert!</span>(cell.get().is_none()); |
| <span class="kw">let </span>value = cell.get_or_try_init(|| -> <span class="prelude-ty">Result</span><i32, ()> { |
| <span class="prelude-val">Ok</span>(<span class="number">92</span>) |
| }); |
| <span class="macro">assert_eq!</span>(value, <span class="prelude-val">Ok</span>(<span class="kw-2">&</span><span class="number">92</span>)); |
| <span class="macro">assert_eq!</span>(cell.get(), <span class="prelude-val">Some</span>(<span class="kw-2">&</span><span class="number">92</span>))</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.take" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1199-1201">source</a><h4 class="code-header">pub fn <a href="#method.take" class="fnname">take</a>(&mut self) -> Option<T></h4></section></summary><div class="docblock"><p>Takes the value out of this <code>OnceCell</code>, moving it back to an uninitialized state.</p> |
| <p>Has no effect and returns <code>None</code> if the <code>OnceCell</code> hasn’t been initialized.</p> |
| <h5 id="examples"><a href="#examples">Examples</a></h5> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>cell: OnceCell<String> = OnceCell::new(); |
| <span class="macro">assert_eq!</span>(cell.take(), <span class="prelude-val">None</span>); |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>cell = OnceCell::new(); |
| cell.set(<span class="string">"hello"</span>.to_string()).unwrap(); |
| <span class="macro">assert_eq!</span>(cell.take(), <span class="prelude-val">Some</span>(<span class="string">"hello"</span>.to_string())); |
| <span class="macro">assert_eq!</span>(cell.get(), <span class="prelude-val">None</span>);</code></pre></div> |
| <p>This method is allowed to violate the invariant of writing to a <code>OnceCell</code> |
| at most once because it requires <code>&mut</code> access to <code>self</code>. As with all |
| interior mutability, <code>&mut</code> access permits arbitrary modification:</p> |
| |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span><span class="kw-2">mut </span>cell: OnceCell<u32> = OnceCell::new(); |
| cell.set(<span class="number">92</span>).unwrap(); |
| cell = OnceCell::new();</code></pre></div> |
| </div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.into_inner" class="method has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#1219-1221">source</a><h4 class="code-header">pub fn <a href="#method.into_inner" class="fnname">into_inner</a>(self) -> Option<T></h4></section></summary><div class="docblock"><p>Consumes the <code>OnceCell</code>, returning the wrapped value. Returns |
| <code>None</code> if the cell was empty.</p> |
| <h5 id="examples-1"><a href="#examples-1">Examples</a></h5> |
| <div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>once_cell::sync::OnceCell; |
| |
| <span class="kw">let </span>cell: OnceCell<String> = OnceCell::new(); |
| <span class="macro">assert_eq!</span>(cell.into_inner(), <span class="prelude-val">None</span>); |
| |
| <span class="kw">let </span>cell = OnceCell::new(); |
| cell.set(<span class="string">"hello"</span>.to_string()).unwrap(); |
| <span class="macro">assert_eq!</span>(cell.into_inner(), <span class="prelude-val">Some</span>(<span class="string">"hello"</span>.to_string()));</code></pre></div> |
| </div></details></div></details></div><h2 id="trait-implementations" class="small-section-header">Trait Implementations<a href="#trait-implementations" class="anchor"></a></h2><div id="trait-implementations-list"><details class="rustdoc-toggle implementors-toggle" open><summary><section id="impl-Clone-for-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#920-934">source</a><a href="#impl-Clone-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T: Clone> Clone for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.clone" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#921-926">source</a><a href="#method.clone" class="anchor"></a><h4 class="code-header">fn <a class="fnname">clone</a>(&self) -> <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h4></section></summary><div class='docblock'>Returns a copy of the value. <a>Read more</a></div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.clone_from" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#928-933">source</a><a href="#method.clone_from" class="anchor"></a><h4 class="code-header">fn <a class="fnname">clone_from</a>(&mut self, source: &Self)</h4></section></summary><div class='docblock'>Performs copy-assignment from <code>source</code>. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle" open><summary><section id="impl-Debug-for-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#911-918">source</a><a href="#impl-Debug-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T: Debug> Debug for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.fmt" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#912-917">source</a><a href="#method.fmt" class="anchor"></a><h4 class="code-header">fn <a class="fnname">fmt</a>(&self, f: &mut Formatter<'_>) -> Result</h4></section></summary><div class='docblock'>Formats the value using the given formatter. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle" open><summary><section id="impl-Default-for-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#905-909">source</a><a href="#impl-Default-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> Default for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.default" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#906-908">source</a><a href="#method.default" class="anchor"></a><h4 class="code-header">fn <a class="fnname">default</a>() -> <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h4></section></summary><div class='docblock'>Returns the “default value” for a type. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle" open><summary><section id="impl-From%3CT%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#936-940">source</a><a href="#impl-From%3CT%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> From<T> for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.from" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#937-939">source</a><a href="#method.from" class="anchor"></a><h4 class="code-header">fn <a class="fnname">from</a>(value: T) -> Self</h4></section></summary><div class='docblock'>Converts to this type from the input type.</div></details></div></details><details class="rustdoc-toggle implementors-toggle" open><summary><section id="impl-PartialEq%3COnceCell%3CT%3E%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#942-946">source</a><a href="#impl-PartialEq%3COnceCell%3CT%3E%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T: PartialEq> PartialEq<<a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T>> for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.eq" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#943-945">source</a><a href="#method.eq" class="anchor"></a><h4 class="code-header">fn <a class="fnname">eq</a>(&self, other: &<a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T>) -> bool</h4></section></summary><div class='docblock'>This method tests for <code>self</code> and <code>other</code> values to be equal, and is used |
| by <code>==</code>. <a>Read more</a></div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.ne" class="method trait-impl has-srclink"><span class="since rightside" title="Stable since Rust version 1.0.0">1.0.0</span><a href="#method.ne" class="anchor"></a><h4 class="code-header">const fn <a class="fnname">ne</a>(&self, other: &Rhs) -> bool</h4></section></summary><div class='docblock'>This method tests for <code>!=</code>. The default implementation is almost always |
| sufficient, and should not be overridden without very good reason. <a>Read more</a></div></details></div></details><section id="impl-Eq-for-OnceCell%3CT%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/once_cell/lib.rs.html#948">source</a><a href="#impl-Eq-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T: Eq> Eq for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T></h3></section></div><h2 id="synthetic-implementations" class="small-section-header">Auto Trait Implementations<a href="#synthetic-implementations" class="anchor"></a></h2><div id="synthetic-implementations-list"><section id="impl-RefUnwindSafe-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-RefUnwindSafe-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> RefUnwindSafe for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T><span class="where fmt-newline">where<br> T: UnwindSafe + RefUnwindSafe,</span></h3></section><section id="impl-Send-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-Send-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> Send for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T><span class="where fmt-newline">where<br> T: Send,</span></h3></section><section id="impl-Sync-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-Sync-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> Sync for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T><span class="where fmt-newline">where<br> T: Send + Sync,</span></h3></section><section id="impl-Unpin-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-Unpin-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> Unpin for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T><span class="where fmt-newline">where<br> T: Unpin,</span></h3></section><section id="impl-UnwindSafe-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-UnwindSafe-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> UnwindSafe for <a class="struct" href="struct.OnceCell.html" title="struct once_cell::sync::OnceCell">OnceCell</a><T><span class="where fmt-newline">where<br> T: UnwindSafe,</span></h3></section></div><h2 id="blanket-implementations" class="small-section-header">Blanket Implementations<a href="#blanket-implementations" class="anchor"></a></h2><div id="blanket-implementations-list"><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Any-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-Any-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> Any for T<span class="where fmt-newline">where<br> T: 'static + ?Sized,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.type_id" class="method trait-impl has-srclink"><a href="#method.type_id" class="anchor"></a><h4 class="code-header">fn <a class="fnname">type_id</a>(&self) -> TypeId</h4></section></summary><div class='docblock'>Gets the <code>TypeId</code> of <code>self</code>. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Borrow%3CT%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-Borrow%3CT%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> Borrow<T> for T<span class="where fmt-newline">where<br> T: ?Sized,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.borrow" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/91522" title="Tracking issue for const_borrow">unstable</a></span><a href="#method.borrow" class="anchor"></a><h4 class="code-header">fn <a class="fnname">borrow</a>(&self) -> &T</h4></section></summary><div class='docblock'>Immutably borrows from an owned value. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-BorrowMut%3CT%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-BorrowMut%3CT%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> BorrowMut<T> for T<span class="where fmt-newline">where<br> T: ?Sized,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.borrow_mut" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/91522" title="Tracking issue for const_borrow">unstable</a></span><a href="#method.borrow_mut" class="anchor"></a><h4 class="code-header">fn <a class="fnname">borrow_mut</a>(&mut self) -> &mut T</h4></section></summary><div class='docblock'>Mutably borrows from an owned value. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-From%3C!%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-From%3C!%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> From<!> for T</h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.from-2" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/88674" title="Tracking issue for const_convert">unstable</a></span><a href="#method.from-2" class="anchor"></a><h4 class="code-header">fn <a class="fnname">from</a>(t: !) -> T</h4></section></summary><div class='docblock'>Converts to this type from the input type.</div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-From%3CT%3E-for-OnceCell%3CT%3E-1" class="impl has-srclink"><a href="#impl-From%3CT%3E-for-OnceCell%3CT%3E-1" class="anchor"></a><h3 class="code-header">impl<T> From<T> for T</h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.from-1" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/88674" title="Tracking issue for const_convert">unstable</a></span><a href="#method.from-1" class="anchor"></a><h4 class="code-header">fn <a class="fnname">from</a>(t: T) -> T</h4></section></summary><div class="docblock"><p>Returns the argument unchanged.</p> |
| </div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Into%3CU%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-Into%3CU%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T, U> Into<U> for T<span class="where fmt-newline">where<br> U: From<T>,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.into" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/88674" title="Tracking issue for const_convert">unstable</a></span><a href="#method.into" class="anchor"></a><h4 class="code-header">fn <a class="fnname">into</a>(self) -> U</h4></section></summary><div class="docblock"><p>Calls <code>U::from(self)</code>.</p> |
| <p>That is, this conversion is whatever the implementation of |
| <code>[From]<T> for U</code> chooses to do.</p> |
| </div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-ToOwned-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-ToOwned-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T> ToOwned for T<span class="where fmt-newline">where<br> T: Clone,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle" open><summary><section id="associatedtype.Owned" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Owned" class="anchor"></a><h4 class="code-header">type <a class="associatedtype">Owned</a> = T</h4></section></summary><div class='docblock'>The resulting type after obtaining ownership.</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.to_owned" class="method trait-impl has-srclink"><a href="#method.to_owned" class="anchor"></a><h4 class="code-header">fn <a class="fnname">to_owned</a>(&self) -> T</h4></section></summary><div class='docblock'>Creates owned data from borrowed data, usually by cloning. <a>Read more</a></div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.clone_into" class="method trait-impl has-srclink"><a href="#method.clone_into" class="anchor"></a><h4 class="code-header">fn <a class="fnname">clone_into</a>(&self, target: &mut T)</h4></section></summary><div class='docblock'>Uses borrowed data to replace owned data, usually by cloning. <a>Read more</a></div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-TryFrom%3CU%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-TryFrom%3CU%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T, U> TryFrom<U> for T<span class="where fmt-newline">where<br> U: Into<T>,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle" open><summary><section id="associatedtype.Error-1" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Error-1" class="anchor"></a><h4 class="code-header">type <a class="associatedtype">Error</a> = Infallible</h4></section></summary><div class='docblock'>The type returned in the event of a conversion error.</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.try_from" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/88674" title="Tracking issue for const_convert">unstable</a></span><a href="#method.try_from" class="anchor"></a><h4 class="code-header">fn <a class="fnname">try_from</a>(value: U) -> Result<T, <T as TryFrom<U>>::Error></h4></section></summary><div class='docblock'>Performs the conversion.</div></details></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-TryInto%3CU%3E-for-OnceCell%3CT%3E" class="impl has-srclink"><a href="#impl-TryInto%3CU%3E-for-OnceCell%3CT%3E" class="anchor"></a><h3 class="code-header">impl<T, U> TryInto<U> for T<span class="where fmt-newline">where<br> U: TryFrom<T>,</span></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle" open><summary><section id="associatedtype.Error" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Error" class="anchor"></a><h4 class="code-header">type <a class="associatedtype">Error</a> = <U as TryFrom<T>>::Error</h4></section></summary><div class='docblock'>The type returned in the event of a conversion error.</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.try_into" class="method trait-impl has-srclink"><span class="since rightside" title="const unstable">const: <a href="https://github.com/rust-lang/rust/issues/88674" title="Tracking issue for const_convert">unstable</a></span><a href="#method.try_into" class="anchor"></a><h4 class="code-header">fn <a class="fnname">try_into</a>(self) -> Result<U, <U as TryFrom<T>>::Error></h4></section></summary><div class='docblock'>Performs the conversion.</div></details></div></details></div></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="once_cell" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
