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