forked from mirror/async-std
40 lines
1.3 KiB
Rust
40 lines
1.3 KiB
Rust
use std::collections::HashSet;
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use std::hash::{BuildHasher, Hash};
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use std::pin::Pin;
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use crate::prelude::*;
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use crate::stream::{self, IntoStream};
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impl<T, H> stream::Extend<T> for HashSet<T, H>
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where
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T: Eq + Hash,
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H: BuildHasher + Default,
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{
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fn extend<'a, S: IntoStream<Item = T> + 'a>(
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&'a mut self,
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stream: S,
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) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
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// The Extend impl for HashSet in the standard library delegates to the internal HashMap.
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// Thus, this impl is just a copy of the async Extend impl for HashMap in this crate.
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let stream = stream.into_stream();
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// The following is adapted from the hashbrown source code:
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// https://github.com/rust-lang/hashbrown/blob/d1ad4fc3aae2ade446738eea512e50b9e863dd0c/src/map.rs#L2470-L2491
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//
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// Keys may be already present or show multiple times in the stream. Reserve the entire
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// hint lower bound if the map is empty. Otherwise reserve half the hint (rounded up), so
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// the map will only resize twice in the worst case.
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let additional = if self.is_empty() {
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stream.size_hint().0
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} else {
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(stream.size_hint().0 + 1) / 2
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};
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self.reserve(additional);
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Box::pin(stream.for_each(move |item| {
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self.insert(item);
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}))
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}
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}
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