Skip to content

Allow replacing HashMap entries #44278

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
bors merged 3 commits into from
Sep 28, 2017
Merged

Allow replacing HashMap entries #44278

Changes from all commits
Commits
Show all changes
3 commits
Select commit Hold shift + click to select a range
e9f01bc
Added a way to retrieve the key out of a HashMap when it's being repl…
Binero Sep 2, 2017
a312b47
Marked `Entry::replace` as unstable.
Binero Sep 3, 2017
d3de465
Addressed @BurntSuchi's remarks regarding Entry::replace
Binero Sep 12, 2017
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
30 changes: 30 additions & 0 deletions src/libstd/collections/hash/map.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -2161,6 +2161,36 @@ impl<'a, K, V> OccupiedEntry<'a, K, V> {
fn take_key(&mut self) -> Option<K> {
self.key.take()
}

/// Replaces the entry, returning the old key and value.
///
/// # Examples
///
/// ```
/// #![feature(map_entry_replace)]
/// use std::collections::HashMap;
/// use std::collections::hash_map::Entry;
///
/// let mut map: HashMap<String, u32> = HashMap::new();
/// map.insert("poneyland".to_string(), 15);
///
/// if let Entry::Occupied(entry) = map.entry("poneyland".to_string()) {
/// let (old_key, old_value): (String, u32) = entry.replace(16);
/// assert_eq!(old_key, "poneyland");
/// assert_eq!(old_value, 15);
/// }
///
/// assert_eq!(map.get("poneyland"), Some(&16));
/// ```
#[unstable(feature = "map_entry_replace", issue = "44286")]
pub fn replace(mut self, value: V) -> (K, V) {
let (old_key, old_value) = self.elem.read_mut();

let old_key = mem::replace(old_key, self.key.unwrap());
Copy link
Contributor

@arthurprs arthurprs Sep 20, 2017

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

One can take the key out of the entry using take_key before replace, so this key.unwrap() can fail. It needs a custom message at least.

let old_value = mem::replace(old_value, value);

(old_key, old_value)
}
}

impl<'a, K: 'a, V: 'a> VacantEntry<'a, K, V> {
Expand Down