async_std/collections/hash_map/
extend.rs

1use std::collections::HashMap;
2use std::hash::{BuildHasher, Hash};
3use std::pin::Pin;
4
5use crate::prelude::*;
6use crate::stream::{self, IntoStream};
7
8impl<K, V, H> stream::Extend<(K, V)> for HashMap<K, V, H>
9where
10    K: Eq + Hash,
11    H: BuildHasher + Default,
12{
13    fn extend<'a, S: IntoStream<Item = (K, V)> + 'a>(
14        &'a mut self,
15        stream: S,
16    ) -> Pin<Box<dyn Future<Output = ()> + 'a>> {
17        let stream = stream.into_stream();
18
19        // The following is adapted from the hashbrown source code:
20        // https://github.com/rust-lang/hashbrown/blob/d1ad4fc3aae2ade446738eea512e50b9e863dd0c/src/map.rs#L2470-L2491
21        //
22        // Keys may be already present or show multiple times in the stream. Reserve the entire
23        // hint lower bound if the map is empty. Otherwise reserve half the hint (rounded up), so
24        // the map will only resize twice in the worst case.
25
26        let additional = if self.is_empty() {
27            stream.size_hint().0
28        } else {
29            (stream.size_hint().0 + 1) / 2
30        };
31        self.reserve(additional);
32
33        Box::pin(stream.for_each(move |(k, v)| {
34            self.insert(k, v);
35        }))
36    }
37}
async_std/collections/hash_map/extend.rs

async_std/collections/hash_map/
extend.rs
