| <!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="Returns a reference to the inner value."><meta name="keywords" content="rust, rustlang, rust-lang, Ref"><title>Ref in tokio::sync::watch - 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 rel="stylesheet" href="../../../normalize.css"><link rel="stylesheet" href="../../../rustdoc.css" id="mainThemeStyle"><link rel="stylesheet" href="../../../ayu.css" disabled><link rel="stylesheet" href="../../../dark.css" disabled><link rel="stylesheet" href="../../../light.css" id="themeStyle"><script id="default-settings" ></script><script src="../../../storage.js"></script><script defer src="sidebar-items.js"></script><script defer src="../../../main.js"></script><noscript><link rel="stylesheet" href="../../../noscript.css"></noscript><link rel="alternate icon" type="image/png" href="../../../favicon-16x16.png"><link rel="alternate icon" type="image/png" href="../../../favicon-32x32.png"><link rel="icon" type="image/svg+xml" href="../../../favicon.svg"></head><body class="rustdoc struct"><!--[if lte IE 11]><div class="warning">This old browser is unsupported and will most likely display funky things.</div><![endif]--><nav class="mobile-topbar"><button class="sidebar-menu-toggle">☰</button><a class="sidebar-logo" href="../../../tokio/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="../../../tokio/index.html"><div class="logo-container"><img class="rust-logo" src="../../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Ref</a></h2><div class="sidebar-elems"><section><h3><a href="#implementations">Methods</a></h3><ul class="block"><li><a href="#method.has_changed">has_changed</a></li></ul><h3><a href="#trait-implementations">Trait Implementations</a></h3><ul class="block"><li><a href="#impl-Debug-for-Ref%3C%27a%2C%20T%3E">Debug</a></li><li><a href="#impl-Deref-for-Ref%3C%27_%2C%20T%3E">Deref</a></li></ul><h3><a href="#synthetic-implementations">Auto Trait Implementations</a></h3><ul class="block"><li><a href="#impl-RefUnwindSafe-for-Ref%3C%27a%2C%20T%3E">RefUnwindSafe</a></li><li><a href="#impl-Send-for-Ref%3C%27a%2C%20T%3E">!Send</a></li><li><a href="#impl-Sync-for-Ref%3C%27a%2C%20T%3E">Sync</a></li><li><a href="#impl-Unpin-for-Ref%3C%27a%2C%20T%3E">Unpin</a></li><li><a href="#impl-UnwindSafe-for-Ref%3C%27a%2C%20T%3E">UnwindSafe</a></li></ul><h3><a href="#blanket-implementations">Blanket Implementations</a></h3><ul class="block"><li><a href="#impl-Any-for-Ref%3C%27a%2C%20T%3E">Any</a></li><li><a href="#impl-Borrow%3CT%3E-for-Ref%3C%27a%2C%20T%3E">Borrow<T></a></li><li><a href="#impl-BorrowMut%3CT%3E-for-Ref%3C%27a%2C%20T%3E">BorrowMut<T></a></li><li><a href="#impl-From%3CT%3E-for-Ref%3C%27a%2C%20T%3E">From<T></a></li><li><a href="#impl-Into%3CU%3E-for-Ref%3C%27a%2C%20T%3E">Into<U></a></li><li><a href="#impl-TryFrom%3CU%3E-for-Ref%3C%27a%2C%20T%3E">TryFrom<U></a></li><li><a href="#impl-TryInto%3CU%3E-for-Ref%3C%27a%2C%20T%3E">TryInto<U></a></li></ul></section><h2><a href="index.html">In tokio::sync::watch</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">tokio</a>::<wbr><a href="../index.html">sync</a>::<wbr><a href="index.html">watch</a>::<wbr><a class="struct" href="#">Ref</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/tokio/sync/watch.rs.html#116-119">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 Ref<'a, T> { /* private fields */ }</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>Returns a reference to the inner value.</p> |
| <p>Outstanding borrows hold a read lock on the inner value. This means that |
| long-lived borrows could cause the producer half to block. It is recommended |
| to keep the borrow as short-lived as possible. Additionally, if you are |
| running in an environment that allows <code>!Send</code> futures, you must ensure that |
| the returned <code>Ref</code> type is never held alive across an <code>.await</code> point, |
| otherwise, it can lead to a deadlock.</p> |
| <p>The priority policy of the lock is dependent on the underlying lock |
| implementation, and this type does not guarantee that any particular policy |
| will be used. In particular, a producer which is waiting to acquire the lock |
| in <code>send</code> might or might not block concurrent calls to <code>borrow</code>, e.g.:</p> |
| <details><summary>Potential deadlock example</summary> |
| <div class="example-wrap"><pre class="language-text"><code>// Task 1 (on thread A) | // Task 2 (on thread B) |
| let _ref1 = rx.borrow(); | |
| | // will block |
| | let _ = tx.send(()); |
| // may deadlock | |
| let _ref2 = rx.borrow(); |</code></pre></div></details></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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a class="srclink rightside" href="../../../src/tokio/sync/watch.rs.html#121-167">source</a><a href="#impl-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T> <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'a, T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.has_changed" class="method has-srclink"><a class="srclink rightside" href="../../../src/tokio/sync/watch.rs.html#164-166">source</a><h4 class="code-header">pub fn <a href="#method.has_changed" class="fnname">has_changed</a>(&self) -> bool</h4></section></summary><div class="docblock"><p>Indicates if the borrowed value is considered as <em>changed</em> since the last |
| time it has been marked as seen.</p> |
| <p>Unlike <a href="struct.Receiver.html#method.has_changed" title="Receiver::has_changed()"><code>Receiver::has_changed()</code></a>, this method does not fail if the channel is closed.</p> |
| <p>When borrowed from the <a href="struct.Sender.html" title="Sender"><code>Sender</code></a> this function will always return <code>false</code>.</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>tokio::sync::watch; |
| |
| <span class="attribute">#[tokio::main] |
| </span><span class="kw">async fn </span>main() { |
| <span class="kw">let </span>(tx, <span class="kw-2">mut </span>rx) = watch::channel(<span class="string">"hello"</span>); |
| |
| tx.send(<span class="string">"goodbye"</span>).unwrap(); |
| <span class="comment">// The sender does never consider the value as changed. |
| </span><span class="macro">assert!</span>(!tx.borrow().has_changed()); |
| |
| <span class="comment">// Drop the sender immediately, just for testing purposes. |
| </span>drop(tx); |
| |
| <span class="comment">// Even if the sender has already been dropped... |
| </span><span class="macro">assert!</span>(rx.has_changed().is_err()); |
| <span class="comment">// ...the modified value is still readable and detected as changed. |
| </span><span class="macro">assert_eq!</span>(<span class="kw-2">*</span>rx.borrow(), <span class="string">"goodbye"</span>); |
| <span class="macro">assert!</span>(rx.borrow().has_changed()); |
| |
| <span class="comment">// Read the changed value and mark it as seen. |
| </span>{ |
| <span class="kw">let </span>received = rx.borrow_and_update(); |
| <span class="macro">assert_eq!</span>(<span class="kw-2">*</span>received, <span class="string">"goodbye"</span>); |
| <span class="macro">assert!</span>(received.has_changed()); |
| <span class="comment">// Release the read lock when leaving this scope. |
| </span>} |
| |
| <span class="comment">// Now the value has already been marked as seen and could |
| // never be modified again (after the sender has been dropped). |
| </span><span class="macro">assert!</span>(!rx.borrow().has_changed()); |
| }</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-Debug-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a class="srclink rightside" href="../../../src/tokio/sync/watch.rs.html#115">source</a><a href="#impl-Debug-for-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T: Debug> Debug for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'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/tokio/sync/watch.rs.html#115">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-Deref-for-Ref%3C%27_%2C%20T%3E" class="impl has-srclink"><a class="srclink rightside" href="../../../src/tokio/sync/watch.rs.html#979-985">source</a><a href="#impl-Deref-for-Ref%3C%27_%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<T> Deref for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'_, T></h3></section></summary><div class="impl-items"><details class="rustdoc-toggle" open><summary><section id="associatedtype.Target" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Target" class="anchor"></a><h4 class="code-header">type <a class="associatedtype">Target</a> = T</h4></section></summary><div class='docblock'>The resulting type after dereferencing.</div></details><details class="rustdoc-toggle method-toggle" open><summary><section id="method.deref" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../../src/tokio/sync/watch.rs.html#982-984">source</a><a href="#method.deref" class="anchor"></a><h4 class="code-header">fn <a class="fnname">deref</a>(&self) -> &T</h4></section></summary><div class='docblock'>Dereferences the value.</div></details></div></details></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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-RefUnwindSafe-for-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T> RefUnwindSafe for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'a, T><span class="where fmt-newline">where<br> T: RefUnwindSafe,</span></h3></section><section id="impl-Send-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-Send-for-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T> !Send for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'a, T></h3></section><section id="impl-Sync-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-Sync-for-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T> Sync for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'a, T><span class="where fmt-newline">where<br> T: Sync,</span></h3></section><section id="impl-Unpin-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-Unpin-for-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T> Unpin for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'a, T></h3></section><section id="impl-UnwindSafe-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-UnwindSafe-for-Ref%3C%27a%2C%20T%3E" class="anchor"></a><h3 class="code-header">impl<'a, T> UnwindSafe for <a class="struct" href="struct.Ref.html" title="struct tokio::sync::watch::Ref">Ref</a><'a, T><span class="where fmt-newline">where<br> T: RefUnwindSafe,</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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-Any-for-Ref%3C%27a%2C%20T%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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-Borrow%3CT%3E-for-Ref%3C%27a%2C%20T%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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-BorrowMut%3CT%3E-for-Ref%3C%27a%2C%20T%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%3CT%3E-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-From%3CT%3E-for-Ref%3C%27a%2C%20T%3E" 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" 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" 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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-Into%3CU%3E-for-Ref%3C%27a%2C%20T%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-TryFrom%3CU%3E-for-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-TryFrom%3CU%3E-for-Ref%3C%27a%2C%20T%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-Ref%3C%27a%2C%20T%3E" class="impl has-srclink"><a href="#impl-TryInto%3CU%3E-for-Ref%3C%27a%2C%20T%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="tokio" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
