| <!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 stream of values produced asynchronously."><meta name="keywords" content="rust, rustlang, rust-lang, Stream"><title>Stream in futures_core::stream - 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 trait"><!--[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="../../futures_core/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="../../futures_core/index.html"><div class="logo-container"><img class="rust-logo" src="../../rust-logo.svg" alt="logo"></div></a><h2 class="location"><a href="#">Stream</a></h2><div class="sidebar-elems"><section><h3><a href="#required-associated-types">Required Associated Types</a></h3><ul class="block"><li><a href="#associatedtype.Item">Item</a></li></ul><h3><a href="#required-methods">Required Methods</a></h3><ul class="block"><li><a href="#tymethod.poll_next">poll_next</a></li></ul><h3><a href="#provided-methods">Provided Methods</a></h3><ul class="block"><li><a href="#method.size_hint">size_hint</a></li></ul><h3><a href="#foreign-impls">Implementations on Foreign Types</a></h3><ul class="block"><li><a href="#impl-Stream-for-%26mut%20S">&mut S</a></li><li><a href="#impl-Stream-for-AssertUnwindSafe%3CS%3E">AssertUnwindSafe<S></a></li><li><a href="#impl-Stream-for-Box%3CS%3E">Box<S></a></li><li><a href="#impl-Stream-for-Pin%3CP%3E">Pin<P></a></li></ul><h3><a href="#implementors">Implementors</a></h3></section><h2><a href="index.html">In futures_core::stream</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">Trait <a href="../index.html">futures_core</a>::<wbr><a href="index.html">stream</a>::<wbr><a class="trait" href="#">Stream</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/futures_core/stream.rs.html#27-98">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 trait"><code>pub trait Stream { |
| type <a href="#associatedtype.Item" class="associatedtype">Item</a>; |
| |
| fn <a href="#tymethod.poll_next" class="fnname">poll_next</a>(<br> self: Pin<&mut Self>,<br> cx: &mut Context<'_><br> ) -> Poll<Option<Self::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a>>>; |
| |
| fn <a href="#method.size_hint" class="fnname">size_hint</a>(&self) -> (usize, Option<usize>) { ... } |
| }</code></pre></div><details class="rustdoc-toggle top-doc" open><summary class="hideme"><span>Expand description</span></summary><div class="docblock"><p>A stream of values produced asynchronously.</p> |
| <p>If <code>Future<Output = T></code> is an asynchronous version of <code>T</code>, then <code>Stream<Item = T></code> is an asynchronous version of <code>Iterator<Item = T></code>. A stream |
| represents a sequence of value-producing events that occur asynchronously to |
| the caller.</p> |
| <p>The trait is modeled after <code>Future</code>, but allows <code>poll_next</code> to be called |
| even after a value has been produced, yielding <code>None</code> once the stream has |
| been fully exhausted.</p> |
| </div></details><h2 id="required-associated-types" class="small-section-header">Required Associated Types<a href="#required-associated-types" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="associatedtype.Item" class="method has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#29">source</a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a></h4></section></summary><div class="docblock"><p>Values yielded by the stream.</p> |
| </div></details></div><h2 id="required-methods" class="small-section-header">Required Methods<a href="#required-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="tymethod.poll_next" class="method has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#66">source</a><h4 class="code-header">fn <a href="#tymethod.poll_next" class="fnname">poll_next</a>(<br> self: Pin<&mut Self>,<br> cx: &mut Context<'_><br>) -> Poll<Option<Self::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a>>></h4></section></summary><div class="docblock"><p>Attempt to pull out the next value of this stream, registering the |
| current task for wakeup if the value is not yet available, and returning |
| <code>None</code> if the stream is exhausted.</p> |
| <h5 id="return-value"><a href="#return-value">Return value</a></h5> |
| <p>There are several possible return values, each indicating a distinct |
| stream state:</p> |
| <ul> |
| <li> |
| <p><code>Poll::Pending</code> means that this stream’s next value is not ready |
| yet. Implementations will ensure that the current task will be notified |
| when the next value may be ready.</p> |
| </li> |
| <li> |
| <p><code>Poll::Ready(Some(val))</code> means that the stream has successfully |
| produced a value, <code>val</code>, and may produce further values on subsequent |
| <code>poll_next</code> calls.</p> |
| </li> |
| <li> |
| <p><code>Poll::Ready(None)</code> means that the stream has terminated, and |
| <code>poll_next</code> should not be invoked again.</p> |
| </li> |
| </ul> |
| <h5 id="panics"><a href="#panics">Panics</a></h5> |
| <p>Once a stream has finished (returned <code>Ready(None)</code> from <code>poll_next</code>), calling its |
| <code>poll_next</code> method again may panic, block forever, or cause other kinds of |
| problems; the <code>Stream</code> trait places no requirements on the effects of |
| such a call. However, as the <code>poll_next</code> method is not marked <code>unsafe</code>, |
| Rust’s usual rules apply: calls must never cause undefined behavior |
| (memory corruption, incorrect use of <code>unsafe</code> functions, or the like), |
| regardless of the stream’s state.</p> |
| <p>If this is difficult to guard against then the <a href="https://docs.rs/futures/0.3/futures/stream/trait.StreamExt.html#method.fuse"><code>fuse</code></a> adapter can be used |
| to ensure that <code>poll_next</code> always returns <code>Ready(None)</code> in subsequent |
| calls.</p> |
| </div></details></div><h2 id="provided-methods" class="small-section-header">Provided Methods<a href="#provided-methods" class="anchor"></a></h2><div class="methods"><details class="rustdoc-toggle method-toggle" open><summary><section id="method.size_hint" class="method has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#95-97">source</a><h4 class="code-header">fn <a href="#method.size_hint" class="fnname">size_hint</a>(&self) -> (usize, Option<usize>)</h4></section></summary><div class="docblock"><p>Returns the bounds on the remaining length of the stream.</p> |
| <p>Specifically, <code>size_hint()</code> returns a tuple where the first element |
| is the lower bound, and the second element is the upper bound.</p> |
| <p>The second half of the tuple that is returned is an [<code>Option</code>]<code><</code>[<code>usize</code>]<code>></code>. |
| A [<code>None</code>] here means that either there is no known upper bound, or the |
| upper bound is larger than [<code>usize</code>].</p> |
| <h5 id="implementation-notes"><a href="#implementation-notes">Implementation notes</a></h5> |
| <p>It is not enforced that a stream implementation yields the declared |
| number of elements. A buggy stream may yield less than the lower bound |
| or more than the upper bound of elements.</p> |
| <p><code>size_hint()</code> is primarily intended to be used for optimizations such as |
| reserving space for the elements of the stream, but must not be |
| trusted to e.g., omit bounds checks in unsafe code. An incorrect |
| implementation of <code>size_hint()</code> should not lead to memory safety |
| violations.</p> |
| <p>That said, the implementation should provide a correct estimation, |
| because otherwise it would be a violation of the trait’s protocol.</p> |
| <p>The default implementation returns <code>(0, </code>[<code>None</code>]<code>)</code> which is correct for any |
| stream.</p> |
| </div></details></div><h2 id="foreign-impls" class="small-section-header">Implementations on Foreign Types<a href="#foreign-impls" class="anchor"></a></h2><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Stream-for-%26mut%20S" class="impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#100-110">source</a><a href="#impl-Stream-for-%26mut%20S" class="anchor"></a><h3 class="code-header">impl<S: ?Sized + <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a> + Unpin> <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a> for &mut S</h3></section></summary><div class="impl-items"><section id="associatedtype.Item-1" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Item-1" class="anchor"></a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = <S as <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a>>::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a></h4></section><section id="method.poll_next" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#103-105">source</a><a href="#method.poll_next" class="anchor"></a><h4 class="code-header">fn <a href="#tymethod.poll_next" class="fnname">poll_next</a>(<br> self: Pin<&mut Self>,<br> cx: &mut Context<'_><br>) -> Poll<Option<Self::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a>>></h4></section><section id="method.size_hint-1" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#107-109">source</a><a href="#method.size_hint-1" class="anchor"></a><h4 class="code-header">fn <a href="#method.size_hint" class="fnname">size_hint</a>(&self) -> (usize, Option<usize>)</h4></section></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Stream-for-Pin%3CP%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#112-126">source</a><a href="#impl-Stream-for-Pin%3CP%3E" class="anchor"></a><h3 class="code-header">impl<P> <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a> for Pin<P><span class="where fmt-newline">where<br> P: DerefMut + Unpin,<br> P::Target: <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a>,</span></h3></section></summary><div class="impl-items"><section id="associatedtype.Item-2" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Item-2" class="anchor"></a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = <<P as Deref>::Target as <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a>>::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a></h4></section><section id="method.poll_next-1" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#119-121">source</a><a href="#method.poll_next-1" class="anchor"></a><h4 class="code-header">fn <a href="#tymethod.poll_next" class="fnname">poll_next</a>(<br> self: Pin<&mut Self>,<br> cx: &mut Context<'_><br>) -> Poll<Option<Self::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a>>></h4></section><section id="method.size_hint-2" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#123-125">source</a><a href="#method.size_hint-2" class="anchor"></a><h4 class="code-header">fn <a href="#method.size_hint" class="fnname">size_hint</a>(&self) -> (usize, Option<usize>)</h4></section></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Stream-for-Box%3CS%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#205-215">source</a><a href="#impl-Stream-for-Box%3CS%3E" class="anchor"></a><h3 class="code-header">impl<S: ?Sized + <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a> + Unpin> <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a> for Box<S></h3></section></summary><div class="impl-items"><section id="associatedtype.Item-3" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Item-3" class="anchor"></a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = <S as <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a>>::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a></h4></section><section id="method.poll_next-2" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#208-210">source</a><a href="#method.poll_next-2" class="anchor"></a><h4 class="code-header">fn <a href="#tymethod.poll_next" class="fnname">poll_next</a>(<br> self: Pin<&mut Self>,<br> cx: &mut Context<'_><br>) -> Poll<Option<Self::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a>>></h4></section><section id="method.size_hint-3" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#212-214">source</a><a href="#method.size_hint-3" class="anchor"></a><h4 class="code-header">fn <a href="#method.size_hint" class="fnname">size_hint</a>(&self) -> (usize, Option<usize>)</h4></section></div></details><details class="rustdoc-toggle implementors-toggle"><summary><section id="impl-Stream-for-AssertUnwindSafe%3CS%3E" class="impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#218-228">source</a><a href="#impl-Stream-for-AssertUnwindSafe%3CS%3E" class="anchor"></a><h3 class="code-header">impl<S: <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a>> <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a> for AssertUnwindSafe<S></h3></section></summary><div class="impl-items"><section id="associatedtype.Item-4" class="associatedtype trait-impl has-srclink"><a href="#associatedtype.Item-4" class="anchor"></a><h4 class="code-header">type <a href="#associatedtype.Item" class="associatedtype">Item</a> = <S as <a class="trait" href="trait.Stream.html" title="trait futures_core::stream::Stream">Stream</a>>::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a></h4></section><section id="method.poll_next-3" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#221-223">source</a><a href="#method.poll_next-3" class="anchor"></a><h4 class="code-header">fn <a href="#tymethod.poll_next" class="fnname">poll_next</a>(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::<a class="associatedtype" href="trait.Stream.html#associatedtype.Item" title="type futures_core::stream::Stream::Item">Item</a>>></h4></section><section id="method.size_hint-4" class="method trait-impl has-srclink"><a class="srclink rightside" href="../../src/futures_core/stream.rs.html#225-227">source</a><a href="#method.size_hint-4" class="anchor"></a><h4 class="code-header">fn <a href="#method.size_hint" class="fnname">size_hint</a>(&self) -> (usize, Option<usize>)</h4></section></div></details><h2 id="implementors" class="small-section-header">Implementors<a href="#implementors" class="anchor"></a></h2><div id="implementors-list"></div><script src="../../implementors/futures_core/stream/trait.Stream.js" data-ignore-extern-crates="core,alloc" async></script></section></div></main><div id="rustdoc-vars" data-root-path="../../" data-current-crate="futures_core" data-themes="ayu,dark,light" data-resource-suffix="" data-rustdoc-version="1.66.0-nightly (5c8bff74b 2022-10-21)" ></div></body></html> |
