async_std/collections/hash_set/
extend.rs

1use std::collections::HashSet;
2use std::hash::{BuildHasher, Hash};
3use std::pin::Pin;
4
5use crate::prelude::*;
6use crate::stream::{self, IntoStream};
7
8impl<T, H> stream::Extend<T> for HashSet<T, H>
9where
10    T: Eq + Hash,
11    H: BuildHasher + Default,
12{
13    fn extend<'a, S: IntoStream<Item = T> + 'a>(
14        &'a mut self,
15        stream: S,
16    ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
17        // The Extend impl for HashSet in the standard library delegates to the internal HashMap.
18        // Thus, this impl is just a copy of the async Extend impl for HashMap in this crate.
19
20        let stream = stream.into_stream();
21
22        // The following is adapted from the hashbrown source code:
23        // https://github.com/rust-lang/hashbrown/blob/d1ad4fc3aae2ade446738eea512e50b9e863dd0c/src/map.rs#L2470-L2491
24        //
25        // Keys may be already present or show multiple times in the stream. Reserve the entire
26        // hint lower bound if the map is empty. Otherwise reserve half the hint (rounded up), so
27        // the map will only resize twice in the worst case.
28
29        let additional = if self.is_empty() {
30            stream.size_hint().0
31        } else {
32            (stream.size_hint().0 + 1) / 2
33        };
34        self.reserve(additional);
35
36        Box::pin(stream.for_each(move |item| {
37            self.insert(item);
38        }))
39    }
40}
async_std/collections/hash_set/extend.rs

async_std/collections/hash_set/
extend.rs
