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</pre><pre class="rust"><code><span class="kw">use </span><span class="kw">super</span>::assert_sink;
<span class="kw">use </span><span class="kw">crate</span>::unfold_state::UnfoldState;
<span class="kw">use </span>core::{future::Future, pin::Pin};
<span class="kw">use </span>futures_core::ready;
<span class="kw">use </span>futures_core::task::{Context, Poll};
<span class="kw">use </span>futures_sink::Sink;
<span class="kw">use </span>pin_project_lite::pin_project;
<span class="macro">pin_project! </span>{
<span class="doccomment">/// Sink for the [`unfold`] function.
</span><span class="attribute">#[derive(Debug)]
#[must_use = <span class="string">&quot;sinks do nothing unless polled&quot;</span>]
</span><span class="kw">pub struct </span>Unfold&lt;T, F, R&gt; {
function: F,
<span class="attribute">#[pin]
</span>state: UnfoldState&lt;T, R&gt;,
}
}
<span class="doccomment">/// Create a sink from a function which processes one item at a time.
///
/// # Examples
///
/// ```
/// # futures::executor::block_on(async {
/// use futures::sink::{self, SinkExt};
///
/// let unfold = sink::unfold(0, |mut sum, i: i32| {
/// async move {
/// sum += i;
/// eprintln!(&quot;{}&quot;, i);
/// Ok::&lt;_, futures::never::Never&gt;(sum)
/// }
/// });
/// futures::pin_mut!(unfold);
/// unfold.send(5).await?;
/// # Ok::&lt;(), futures::never::Never&gt;(()) }).unwrap();
/// ```
</span><span class="kw">pub fn </span>unfold&lt;T, F, R, Item, E&gt;(init: T, function: F) -&gt; Unfold&lt;T, F, R&gt;
<span class="kw">where
</span>F: FnMut(T, Item) -&gt; R,
R: Future&lt;Output = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
{
assert_sink::&lt;Item, E, <span class="kw">_</span>&gt;(Unfold { function, state: UnfoldState::Value { value: init } })
}
<span class="kw">impl</span>&lt;T, F, R, Item, E&gt; Sink&lt;Item&gt; <span class="kw">for </span>Unfold&lt;T, F, R&gt;
<span class="kw">where
</span>F: FnMut(T, Item) -&gt; R,
R: Future&lt;Output = <span class="prelude-ty">Result</span>&lt;T, E&gt;&gt;,
{
<span class="kw">type </span>Error = E;
<span class="kw">fn </span>poll_ready(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="prelude-ty">Result</span>&lt;(), <span class="self">Self</span>::Error&gt;&gt; {
<span class="self">self</span>.poll_flush(cx)
}
<span class="kw">fn </span>start_send(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, item: Item) -&gt; <span class="prelude-ty">Result</span>&lt;(), <span class="self">Self</span>::Error&gt; {
<span class="kw">let </span><span class="kw-2">mut </span>this = <span class="self">self</span>.project();
<span class="kw">let </span>future = <span class="kw">match </span>this.state.as_mut().take_value() {
<span class="prelude-val">Some</span>(value) =&gt; (this.function)(value, item),
<span class="prelude-val">None </span>=&gt; <span class="macro">panic!</span>(<span class="string">&quot;start_send called without poll_ready being called first&quot;</span>),
};
this.state.set(UnfoldState::Future { future });
<span class="prelude-val">Ok</span>(())
}
<span class="kw">fn </span>poll_flush(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="prelude-ty">Result</span>&lt;(), <span class="self">Self</span>::Error&gt;&gt; {
<span class="kw">let </span><span class="kw-2">mut </span>this = <span class="self">self</span>.project();
Poll::Ready(<span class="kw">if let </span><span class="prelude-val">Some</span>(future) = this.state.as_mut().project_future() {
<span class="kw">match </span><span class="macro">ready!</span>(future.poll(cx)) {
<span class="prelude-val">Ok</span>(state) =&gt; {
this.state.set(UnfoldState::Value { value: state });
<span class="prelude-val">Ok</span>(())
}
<span class="prelude-val">Err</span>(err) =&gt; {
this.state.set(UnfoldState::Empty);
<span class="prelude-val">Err</span>(err)
}
}
} <span class="kw">else </span>{
<span class="prelude-val">Ok</span>(())
})
}
<span class="kw">fn </span>poll_close(<span class="self">self</span>: Pin&lt;<span class="kw-2">&amp;mut </span><span class="self">Self</span>&gt;, cx: <span class="kw-2">&amp;mut </span>Context&lt;<span class="lifetime">&#39;_</span>&gt;) -&gt; Poll&lt;<span class="prelude-ty">Result</span>&lt;(), <span class="self">Self</span>::Error&gt;&gt; {
<span class="self">self</span>.poll_flush(cx)
}
}
</code></pre></div>
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