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</pre><pre class="rust">
<span class="kw">use</span> <span class="kw">super</span>::<span class="kw">super</span><span class="ident">::plumbing</span>::<span class="kw-2">*</span>;
<span class="kw">use</span> <span class="ident">std::marker::PhantomData</span>;
<span class="kw">use</span> <span class="ident">std::mem::MaybeUninit</span>;
<span class="kw">use</span> <span class="ident">std::ptr</span>;
<span class="kw">use</span> <span class="ident">std::slice</span>;
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct</span> <span class="ident">CollectConsumer</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span>: <span class="ident">Send</span><span class="op">></span> {
<span class="doccomment">/// A slice covering the target memory, not yet initialized!</span>
<span class="ident">target</span>: <span class="kw-2">&</span><span class="lifetime">'c</span> <span class="kw-2">mut</span> [<span class="ident">MaybeUninit</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>],
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'c</span><span class="op">></span> <span class="ident">CollectConsumer</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// The target memory is considered uninitialized, and will be</span>
<span class="doccomment">/// overwritten without reading or dropping existing values.</span>
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn</span> <span class="ident">new</span>(<span class="ident">target</span>: <span class="kw-2">&</span><span class="lifetime">'c</span> <span class="kw-2">mut</span> [<span class="ident">MaybeUninit</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>]) <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="ident">CollectConsumer</span> { <span class="ident">target</span> }
}
}
<span class="doccomment">/// CollectResult represents an initialized part of the target slice.</span>
<span class="doccomment">///</span>
<span class="doccomment">/// This is a proxy owner of the elements in the slice; when it drops,</span>
<span class="doccomment">/// the elements will be dropped, unless its ownership is released before then.</span>
<span class="attribute">#[<span class="ident">must_use</span>]</span>
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct</span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// A slice covering the target memory, initialized up to our separate `len`.</span>
<span class="ident">target</span>: <span class="kw-2">&</span><span class="lifetime">'c</span> <span class="kw-2">mut</span> [<span class="ident">MaybeUninit</span><span class="op"><</span><span class="ident">T</span><span class="op">></span>],
<span class="doccomment">/// The current initialized length in `target`</span>
<span class="ident">len</span>: <span class="ident">usize</span>,
<span class="doccomment">/// Lifetime invariance guarantees that the data flows from consumer to result,</span>
<span class="doccomment">/// especially for the `scope_fn` callback in `Collect::with_consumer`.</span>
<span class="ident">invariant_lifetime</span>: <span class="ident">PhantomData</span><span class="op"><</span><span class="kw-2">&</span><span class="lifetime">'c</span> <span class="kw-2">mut</span> <span class="kw-2">&</span><span class="lifetime">'c</span> <span class="kw-2">mut</span> [<span class="ident">T</span>]<span class="op">></span>,
}
<span class="kw">unsafe</span> <span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Send</span> <span class="kw">for</span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> <span class="kw">where</span> <span class="ident">T</span>: <span class="ident">Send</span> {}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="doccomment">/// The current length of the collect result</span>
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn</span> <span class="ident">len</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">usize</span> {
<span class="self">self</span>.<span class="ident">len</span>
}
<span class="doccomment">/// Release ownership of the slice of elements, and return the length</span>
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">fn</span> <span class="ident">release_ownership</span>(<span class="kw-2">mut</span> <span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">usize</span> {
<span class="kw">let</span> <span class="ident">ret</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">len</span>;
<span class="self">self</span>.<span class="ident">len</span> <span class="op">=</span> <span class="number">0</span>;
<span class="ident">ret</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Drop</span> <span class="kw">for</span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">drop</span>(<span class="kw-2">&</span><span class="kw-2">mut</span> <span class="self">self</span>) {
<span class="comment">// Drop the first `self.len` elements, which have been recorded</span>
<span class="comment">// to be initialized by the folder.</span>
<span class="kw">unsafe</span> {
<span class="comment">// TODO: use `MaybeUninit::slice_as_mut_ptr`</span>
<span class="kw">let</span> <span class="ident">start</span> <span class="op">=</span> <span class="self">self</span>.<span class="ident">target</span>.<span class="ident">as_mut_ptr</span>() <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">T</span>;
<span class="ident">ptr::drop_in_place</span>(<span class="ident">slice::from_raw_parts_mut</span>(<span class="ident">start</span>, <span class="self">self</span>.<span class="ident">len</span>));
}
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'c</span><span class="op">></span> <span class="ident">Consumer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">CollectConsumer</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="ident">Folder</span> <span class="op">=</span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span>;
<span class="kw">type</span> <span class="ident">Reducer</span> <span class="op">=</span> <span class="ident">CollectReducer</span>;
<span class="kw">type</span> <span class="prelude-ty">Result</span> <span class="op">=</span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span>;
<span class="kw">fn</span> <span class="ident">split_at</span>(<span class="self">self</span>, <span class="ident">index</span>: <span class="ident">usize</span>) <span class="op">-</span><span class="op">></span> (<span class="self">Self</span>, <span class="self">Self</span>, <span class="ident">CollectReducer</span>) {
<span class="kw">let</span> <span class="ident">CollectConsumer</span> { <span class="ident">target</span> } <span class="op">=</span> <span class="self">self</span>;
<span class="comment">// Produce new consumers. Normal slicing ensures that the</span>
<span class="comment">// memory range given to each consumer is disjoint.</span>
<span class="kw">let</span> (<span class="ident">left</span>, <span class="ident">right</span>) <span class="op">=</span> <span class="ident">target</span>.<span class="ident">split_at_mut</span>(<span class="ident">index</span>);
(
<span class="ident">CollectConsumer::new</span>(<span class="ident">left</span>),
<span class="ident">CollectConsumer::new</span>(<span class="ident">right</span>),
<span class="ident">CollectReducer</span>,
)
}
<span class="kw">fn</span> <span class="ident">into_folder</span>(<span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span><span class="ident">::Folder</span> {
<span class="comment">// Create a result/folder that consumes values and writes them</span>
<span class="comment">// into target. The initial result has length 0.</span>
<span class="ident">CollectResult</span> {
<span class="ident">target</span>: <span class="self">self</span>.<span class="ident">target</span>,
<span class="ident">len</span>: <span class="number">0</span>,
<span class="ident">invariant_lifetime</span>: <span class="ident">PhantomData</span>,
}
}
<span class="kw">fn</span> <span class="ident">full</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="bool-val">false</span>
}
}
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'c</span><span class="op">></span> <span class="ident">Folder</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">type</span> <span class="prelude-ty">Result</span> <span class="op">=</span> <span class="self">Self</span>;
<span class="kw">fn</span> <span class="ident">consume</span>(<span class="kw-2">mut</span> <span class="self">self</span>, <span class="ident">item</span>: <span class="ident">T</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="kw">let</span> <span class="ident">dest</span> <span class="op">=</span> <span class="self">self</span>
.<span class="ident">target</span>
.<span class="ident">get_mut</span>(<span class="self">self</span>.<span class="ident">len</span>)
.<span class="ident">expect</span>(<span class="string">"too many values pushed to consumer"</span>);
<span class="comment">// Write item and increase the initialized length</span>
<span class="kw">unsafe</span> {
<span class="ident">dest</span>.<span class="ident">as_mut_ptr</span>().<span class="ident">write</span>(<span class="ident">item</span>);
<span class="self">self</span>.<span class="ident">len</span> <span class="op">+</span><span class="op">=</span> <span class="number">1</span>;
}
<span class="self">self</span>
}
<span class="kw">fn</span> <span class="ident">complete</span>(<span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span><span class="ident">::Result</span> {
<span class="comment">// NB: We don't explicitly check that the local writes were complete,</span>
<span class="comment">// but Collect will assert the total result length in the end.</span>
<span class="self">self</span>
}
<span class="kw">fn</span> <span class="ident">full</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="ident">bool</span> {
<span class="bool-val">false</span>
}
}
<span class="doccomment">/// Pretend to be unindexed for `special_collect_into_vec`,</span>
<span class="doccomment">/// but we should never actually get used that way...</span>
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span>: <span class="ident">Send</span> <span class="op">+</span> <span class="lifetime">'c</span><span class="op">></span> <span class="ident">UnindexedConsumer</span><span class="op"><</span><span class="ident">T</span><span class="op">></span> <span class="kw">for</span> <span class="ident">CollectConsumer</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="kw">fn</span> <span class="ident">split_off_left</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span> {
<span class="macro">unreachable!</span>(<span class="string">"CollectConsumer must be indexed!"</span>)
}
<span class="kw">fn</span> <span class="ident">to_reducer</span>(<span class="kw-2">&</span><span class="self">self</span>) <span class="op">-</span><span class="op">></span> <span class="self">Self</span><span class="ident">::Reducer</span> {
<span class="ident">CollectReducer</span>
}
}
<span class="doccomment">/// CollectReducer combines adjacent chunks; the result must always</span>
<span class="doccomment">/// be contiguous so that it is one combined slice.</span>
<span class="kw">pub</span>(<span class="kw">super</span>) <span class="kw">struct</span> <span class="ident">CollectReducer</span>;
<span class="kw">impl</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> <span class="ident">Reducer</span><span class="op"><</span><span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span><span class="op">></span> <span class="kw">for</span> <span class="ident">CollectReducer</span> {
<span class="kw">fn</span> <span class="ident">reduce</span>(
<span class="self">self</span>,
<span class="kw-2">mut</span> <span class="ident">left</span>: <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span>,
<span class="ident">right</span>: <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span>,
) <span class="op">-</span><span class="op">></span> <span class="ident">CollectResult</span><span class="op"><</span><span class="lifetime">'c</span>, <span class="ident">T</span><span class="op">></span> {
<span class="comment">// Merge if the CollectResults are adjacent and in left to right order</span>
<span class="comment">// else: drop the right piece now and total length will end up short in the end,</span>
<span class="comment">// when the correctness of the collected result is asserted.</span>
<span class="kw">let</span> <span class="ident">left_end</span> <span class="op">=</span> <span class="ident">left</span>.<span class="ident">target</span>[<span class="ident">left</span>.<span class="ident">len</span>..].<span class="ident">as_ptr</span>();
<span class="kw">if</span> <span class="ident">left_end</span> <span class="op">=</span><span class="op">=</span> <span class="ident">right</span>.<span class="ident">target</span>.<span class="ident">as_ptr</span>() {
<span class="kw">let</span> <span class="ident">len</span> <span class="op">=</span> <span class="ident">left</span>.<span class="ident">len</span> <span class="op">+</span> <span class="ident">right</span>.<span class="ident">release_ownership</span>();
<span class="kw">unsafe</span> {
<span class="ident">left</span>.<span class="ident">target</span> <span class="op">=</span> <span class="ident">slice::from_raw_parts_mut</span>(<span class="ident">left</span>.<span class="ident">target</span>.<span class="ident">as_mut_ptr</span>(), <span class="ident">len</span>);
}
<span class="ident">left</span>.<span class="ident">len</span> <span class="op">=</span> <span class="ident">len</span>;
}
<span class="ident">left</span>
}
}
</pre></div>
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