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Add reinsert to RawOccupiedEntryMut #450

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Add reinsert to RawOccupiedEntryMut #450

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190 changes: 190 additions & 0 deletions src/map.rs
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Expand Up @@ -3942,6 +3942,168 @@ impl<'a, K, V, S, A: Allocator + Clone> RawOccupiedEntryMut<'a, K, V, S, A> {
}
}

impl<'a, K: Eq, V, S, A: Allocator + Clone> RawOccupiedEntryMut<'a, K, V, S, A> {
/// Reinserts the entry into the map.
///
/// # Errors
///
/// If the map already has an entry with this entry's key, nothing is
/// updated, and an error is returned.
///
/// # Examples
///
/// ```
/// use hashbrown::hash_map::{HashMap, RawEntryMut};
///
/// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
///
/// match map.raw_entry_mut().from_key(&"b") {
/// RawEntryMut::Occupied(mut o) => {
/// o.insert_key("c");
/// o.reinsert().unwrap();
/// },
/// RawEntryMut::Vacant(v) => panic!(),
/// }
///
/// assert_eq!(map[&"c"], 200);
/// ```
#[cfg_attr(feature = "inline-more", inline)]
pub fn reinsert(&mut self) -> Result<(), ReinsertError>
where
K: Hash,
S: BuildHasher,
{
let hash = make_hash::<K, S>(self.hash_builder, self.key());
self.reinsert_hashed_nocheck(hash)
}

/// Reinserts the entry into the map.
///
/// # Errors
///
/// If the map already has an entry with this entry's key, nothing is
/// updated, and an error is returned.
///
/// # Examples
///
/// ```
/// use core::hash::{BuildHasher, Hash};
/// use hashbrown::hash_map::{HashMap, RawEntryMut};
///
/// fn compute_hash<K: Hash + ?Sized, S: BuildHasher>(hash_builder: &S, key: &K) -> u64 {
/// use core::hash::Hasher;
/// let mut state = hash_builder.build_hasher();
/// key.hash(&mut state);
/// state.finish()
/// }
///
/// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
/// let old_key = "b";
/// let hasher = map.hasher().clone();
/// let old_hash = compute_hash(&hasher, &old_key);
///
/// match map.raw_entry_mut().from_key_hashed_nocheck(old_hash, &old_key) {
/// RawEntryMut::Occupied(mut o) => {
/// let key = "c";
/// let hash = compute_hash(&hasher, &key);
/// o.insert_key(key);
/// o.reinsert_hashed_nocheck(hash).unwrap();
/// }
/// RawEntryMut::Vacant(v) => panic!()
/// }
///
/// assert_eq!(map[&"c"], 200);
/// ```
#[cfg_attr(feature = "inline-more", inline)]
#[allow(clippy::shadow_unrelated)]
pub fn reinsert_hashed_nocheck(&mut self, hash: u64) -> Result<(), ReinsertError>
where
K: Hash,
S: BuildHasher,
{
let key = unsafe { &self.elem.as_ref().0 };
let hasher = make_hasher::<_, V, S>(self.hash_builder);
let slot = match self
.table
.find_or_find_insert_slot(hash, equivalent_key(key), hasher)
{
Ok(bucket) if bucket.as_ptr() == self.elem.as_ptr() => return Ok(()),
Ok(_bucket) => return Err(ReinsertError),
Err(slot) => slot,
};
unsafe {
let value = self.table.remove(self.elem.clone()).0;
self.elem = self.table.insert_in_slot(hash, slot, value);
}
Ok(())
}

/// Reinserts the entry with a new key using a custom hash function.
///
/// # Errors
///
/// If the map already had the new key present, nothing is updated, and
/// an error is returned.
///
/// # Examples
///
/// ```
/// use core::hash::{BuildHasher, Hash};
/// use hashbrown::hash_map::{HashMap, RawEntryMut};
///
/// fn make_hasher<K, S>(hash_builder: &S) -> impl Fn(&K) -> u64 + '_
/// where
/// K: Hash + ?Sized,
/// S: BuildHasher,
/// {
/// move |key: &K| {
/// use core::hash::Hasher;
/// let mut state = hash_builder.build_hasher();
/// key.hash(&mut state);
/// state.finish()
/// }
/// }
///
/// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
/// let old_key = "b";
/// let hash_builder = map.hasher().clone();
/// let hasher = make_hasher(&hash_builder);
/// let old_hash = hasher(&old_key);
///
/// match map.raw_entry_mut().from_hash(old_hash, |q| q == &old_key) {
/// RawEntryMut::Occupied(mut o) => {
/// let key = "c";
/// let hash = hasher(&key);
/// o.insert_key(key);
/// o.reinsert_with_hasher(hash, hasher).unwrap();
/// },
/// RawEntryMut::Vacant(v) => panic!(),
/// }
///
/// assert_eq!(map[&"c"], 200);
/// ```
#[cfg_attr(feature = "inline-more", inline)]
pub fn reinsert_with_hasher<H>(&mut self, hash: u64, hasher: H) -> Result<(), ReinsertError>
where
H: Fn(&K) -> u64,
{
let key = unsafe { &self.elem.as_ref().0 };
let slot = match self
.table
.find_or_find_insert_slot(hash, equivalent_key(key), |x| hasher(&x.0))
{
Ok(bucket) if bucket.as_ptr() == self.elem.as_ptr() => return Ok(()),
Ok(_bucket) => return Err(ReinsertError),
Err(slot) => slot,
};
unsafe {
let value = self.table.remove(self.elem.clone()).0;
self.elem = self.table.insert_in_slot(hash, slot, value);
}
Ok(())
}
}

impl<'a, K, V, S, A: Allocator + Clone> RawVacantEntryMut<'a, K, V, S, A> {
/// Sets the value of the entry with the VacantEntry's key,
/// and returns a mutable reference to it.
Expand Down Expand Up @@ -4627,6 +4789,34 @@ impl<'a, K: Debug, V: Debug, S, A: Allocator + Clone> fmt::Display
}
}

/// An error returned by [`reinsert`](RawOccupiedEntryMut::reinsert) when an
/// entry could not be reinserted because the map already contains an entry
/// with the new key.
///
/// # Examples
///
/// ```
/// use hashbrown::hash_map::{HashMap, RawEntryMut, ReinsertError};
///
/// let mut map: HashMap<&str, u32> = [("a", 100), ("b", 200)].into();
///
/// match map.raw_entry_mut().from_key(&"b") {
/// RawEntryMut::Occupied(mut o) => {
/// o.insert_key("a");
/// assert_eq!(o.reinsert(), Err(ReinsertError));
/// }
/// RawEntryMut::Vacant(v) => panic!(),
/// }
/// ```
#[derive(PartialEq, Eq, Debug)]
pub struct ReinsertError;

impl fmt::Display for ReinsertError {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.write_str("failed to reinsert entry, map already has entry with new key")
}
}

impl<'a, K, V, S, A: Allocator + Clone> IntoIterator for &'a HashMap<K, V, S, A> {
type Item = (&'a K, &'a V);
type IntoIter = Iter<'a, K, V>;
Expand Down