68c9135913
- Remove duplicate tool header (lib.rs already prints it) - Add newline before timing footer for visual separation - Remove spinner animation (incompatible with update_tool_output_line) - Change shell command format to " > `cmd` ..." with 60 char width
413 lines
29 KiB
HTML
413 lines
29 KiB
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<p>Provides two macros, <code>stream!</code> and <code>try_stream!</code>, allowing the caller to
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trait. The <code>Item</code> associated type is the type of the values yielded from the
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|
||
<a href="https://docs.rs/futures-core/*/futures_core/stream/trait.Stream.html"><code>Stream</code></a> trait, but the <code>Item</code> associated type is <code>Result<T, Error></code>. The
|
||
<code>try_stream!</code> macro supports using <code>?</code> notation as part of the
|
||
implementation.</p>
|
||
<h2 id="usage"><a class="doc-anchor" href="#usage">§</a>Usage</h2>
|
||
<p>A basic stream yielding numbers. Values are yielded using the <code>yield</code>
|
||
keyword. The stream block must return <code>()</code>.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>async_stream::stream;
|
||
|
||
<span class="kw">use </span>futures_util::pin_mut;
|
||
<span class="kw">use </span>futures_util::stream::StreamExt;
|
||
|
||
<span class="attr">#[tokio::main]
|
||
</span><span class="kw">async fn </span>main() {
|
||
<span class="kw">let </span>s = <span class="macro">stream!</span> {
|
||
<span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">3 </span>{
|
||
<span class="kw">yield </span>i;
|
||
}
|
||
};
|
||
|
||
<span class="macro">pin_mut!</span>(s); <span class="comment">// needed for iteration
|
||
|
||
</span><span class="kw">while let </span><span class="prelude-val">Some</span>(value) = s.next().<span class="kw">await </span>{
|
||
<span class="macro">println!</span>(<span class="string">"got {}"</span>, value);
|
||
}
|
||
}</code></pre></div>
|
||
<p>Streams may be returned by using <code>impl Stream<Item = T></code>:</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>async_stream::stream;
|
||
|
||
<span class="kw">use </span>futures_core::stream::Stream;
|
||
<span class="kw">use </span>futures_util::pin_mut;
|
||
<span class="kw">use </span>futures_util::stream::StreamExt;
|
||
|
||
<span class="kw">fn </span>zero_to_three() -> <span class="kw">impl </span>Stream<Item = u32> {
|
||
<span class="macro">stream!</span> {
|
||
<span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">3 </span>{
|
||
<span class="kw">yield </span>i;
|
||
}
|
||
}
|
||
}
|
||
|
||
<span class="attr">#[tokio::main]
|
||
</span><span class="kw">async fn </span>main() {
|
||
<span class="kw">let </span>s = zero_to_three();
|
||
<span class="macro">pin_mut!</span>(s); <span class="comment">// needed for iteration
|
||
|
||
</span><span class="kw">while let </span><span class="prelude-val">Some</span>(value) = s.next().<span class="kw">await </span>{
|
||
<span class="macro">println!</span>(<span class="string">"got {}"</span>, value);
|
||
}
|
||
}</code></pre></div>
|
||
<p>Streams may be implemented in terms of other streams - <code>async-stream</code> provides <code>for await</code>
|
||
syntax to assist with this:</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>async_stream::stream;
|
||
|
||
<span class="kw">use </span>futures_core::stream::Stream;
|
||
<span class="kw">use </span>futures_util::pin_mut;
|
||
<span class="kw">use </span>futures_util::stream::StreamExt;
|
||
|
||
<span class="kw">fn </span>zero_to_three() -> <span class="kw">impl </span>Stream<Item = u32> {
|
||
<span class="macro">stream!</span> {
|
||
<span class="kw">for </span>i <span class="kw">in </span><span class="number">0</span>..<span class="number">3 </span>{
|
||
<span class="kw">yield </span>i;
|
||
}
|
||
}
|
||
}
|
||
|
||
<span class="kw">fn </span>double<S: Stream<Item = u32>>(input: S)
|
||
-> <span class="kw">impl </span>Stream<Item = u32>
|
||
{
|
||
<span class="macro">stream!</span> {
|
||
<span class="kw">for await </span>value <span class="kw">in </span>input {
|
||
<span class="kw">yield </span>value * <span class="number">2</span>;
|
||
}
|
||
}
|
||
}
|
||
|
||
<span class="attr">#[tokio::main]
|
||
</span><span class="kw">async fn </span>main() {
|
||
<span class="kw">let </span>s = double(zero_to_three());
|
||
<span class="macro">pin_mut!</span>(s); <span class="comment">// needed for iteration
|
||
|
||
</span><span class="kw">while let </span><span class="prelude-val">Some</span>(value) = s.next().<span class="kw">await </span>{
|
||
<span class="macro">println!</span>(<span class="string">"got {}"</span>, value);
|
||
}
|
||
}</code></pre></div>
|
||
<p>Rust try notation (<code>?</code>) can be used with the <code>try_stream!</code> macro. The <code>Item</code>
|
||
of the returned stream is <code>Result</code> with <code>Ok</code> being the value yielded and
|
||
<code>Err</code> the error type returned by <code>?</code>.</p>
|
||
|
||
<div class="example-wrap"><pre class="rust rust-example-rendered"><code><span class="kw">use </span>tokio::net::{TcpListener, TcpStream};
|
||
|
||
<span class="kw">use </span>async_stream::try_stream;
|
||
<span class="kw">use </span>futures_core::stream::Stream;
|
||
|
||
<span class="kw">use </span>std::io;
|
||
<span class="kw">use </span>std::net::SocketAddr;
|
||
|
||
<span class="kw">fn </span>bind_and_accept(addr: SocketAddr)
|
||
-> <span class="kw">impl </span>Stream<Item = io::Result<TcpStream>>
|
||
{
|
||
<span class="macro">try_stream!</span> {
|
||
<span class="kw">let </span><span class="kw-2">mut </span>listener = TcpListener::bind(addr).<span class="kw">await</span><span class="question-mark">?</span>;
|
||
|
||
<span class="kw">loop </span>{
|
||
<span class="kw">let </span>(stream, addr) = listener.accept().<span class="kw">await</span><span class="question-mark">?</span>;
|
||
<span class="macro">println!</span>(<span class="string">"received on {:?}"</span>, addr);
|
||
<span class="kw">yield </span>stream;
|
||
}
|
||
}
|
||
}</code></pre></div><h2 id="implementation"><a class="doc-anchor" href="#implementation">§</a>Implementation</h2>
|
||
<p>The <code>stream!</code> and <code>try_stream!</code> macros are implemented using proc macros.
|
||
The macro searches the syntax tree for instances of <code>yield $expr</code> and
|
||
transforms them into <code>sender.send($expr).await</code>.</p>
|
||
<p>The stream uses a lightweight sender to send values from the stream
|
||
implementation to the caller. When entering the stream, an <code>Option<T></code> is
|
||
stored on the stack. A pointer to the cell is stored in a thread local and
|
||
<code>poll</code> is called on the async block. When <code>poll</code> returns.
|
||
<code>sender.send(value)</code> stores the value that cell and yields back to the
|
||
caller.</p>
|
||
</div></details><h2 id="macros" class="section-header">Macros<a href="#macros" class="anchor">§</a></h2><dl class="item-table"><dt><a class="macro" href="macro.stream.html" title="macro async_stream::stream">stream</a></dt><dd>Asynchronous stream</dd><dt><a class="macro" href="macro.try_stream.html" title="macro async_stream::try_stream">try_<wbr>stream</a></dt><dd>Asynchronous fallible stream</dd></dl></section><section id="alternative-display" class="content hidden"></section><section id="not-displayed" class="hidden"><section id="search"><div class="main-heading search-results-main-heading"><nav class="sub">
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