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feat: Add filter to HashSet/Table/Map #588

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feat: Add filter to HashSet/Table/Map #588

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f68b09c
feat: Add retain_with_break to HashSet/Table/Map
Nov 14, 2024
35b4479
feat: Add filter to HashSet/Table/Map
Nov 14, 2024
cb750fe
Merge branch 'rust-lang:master' into master
tugtugtug Nov 25, 2024
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88 changes: 88 additions & 0 deletions src/map.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -929,6 +929,69 @@ impl<K, V, S, A: Allocator> HashMap<K, V, S, A> {
}
}

/// Iterates over elements, applying the specified `ControlFlow` predicate to each
///
/// ### Element Fate
/// - Kept if `f(&k, &mut v)` returns `ControlFlow::<Any>(true)`
/// - Removed if `f(&k, &mut v)` returns `ControlFlow::<Any>(false)`
///
/// ### Iteration Control
/// - Continue iterating if `f(&k, &mut v)` returns `ControlFlow::Continue`
/// - Abort iteration immediately (after applying the element fate) if `f(&k, &mut v)`
/// returns `ControlFlow::Break`
///
/// The elements are visited in unsorted (and unspecified) order.
///
/// # Examples
///
/// ```
/// use hashbrown::HashMap;
/// use core::ops::ControlFlow;
///
/// let mut map: HashMap<i32, i32> = (0..8).map(|x|(x, x*10)).collect();
/// assert_eq!(map.len(), 8);
/// let mut removed = 0;
/// map.filter(|&k, _| if removed < 3 {
/// if k % 2 == 0 {
/// ControlFlow::Continue(true)
/// } else {
/// removed += 1;
/// ControlFlow::Continue(false)
/// }
/// } else {
/// // keep this item and break
/// ControlFlow::Break(true)
/// });
///
/// // We can see, that the number of elements inside map is changed and the
/// // length matches when we have aborted the iteration with the return of `ControlFlow::Break`
/// assert_eq!(map.len(), 5);
/// ```
pub fn filter<F>(&mut self, mut f: F)
where
F: FnMut(&K, &mut V) -> core::ops::ControlFlow<bool, bool>,
{
// Here we only use `iter` as a temporary, preventing use-after-free
unsafe {
for item in self.table.iter() {
let &mut (ref key, ref mut value) = item.as_mut();
match f(key, value) {
core::ops::ControlFlow::Continue(kept) => {
if !kept {
self.table.erase(item);
}
}
core::ops::ControlFlow::Break(kept) => {
if !kept {
self.table.erase(item);
}
break;
}
}
}
}
}

/// Drains elements which are true under the given predicate,
/// and returns an iterator over the removed items.
///
Expand Down Expand Up @@ -5909,6 +5972,31 @@ mod test_map {
assert_eq!(map[&6], 60);
}

#[test]
fn test_filter() {
let mut map: HashMap<i32, i32> = (0..100).map(|x| (x, x * 10)).collect();
// looping and removing any key > 50, but stop after 40 removed
let mut removed = 0;
map.filter(|&k, _| {
if k > 50 {
removed += 1;
if removed < 40 {
core::ops::ControlFlow::Continue(false)
} else {
// remove this item and break
core::ops::ControlFlow::Break(false)
}
} else {
core::ops::ControlFlow::Continue(true)
}
});
assert_eq!(map.len(), 60);
// check nothing up to 50 is removed
for k in 0..=50 {
assert_eq!(map[&k], k * 10);
}
}

#[test]
fn test_extract_if() {
{
Expand Down
65 changes: 65 additions & 0 deletions src/set.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -372,6 +372,47 @@ impl<T, S, A: Allocator> HashSet<T, S, A> {
self.map.retain(|k, _| f(k));
}

/// Iterates over elements, applying the specified `ControlFlow` predicate to each
///
/// ### Element Fate
/// - Kept if `f(&e)` returns `ControlFlow::<Any>(true)`
/// - Removed if `f(&e)` returns `ControlFlow::<Any>(false)`
///
/// ### Iteration Control
/// - Continue iterating if `f(&e)` returns `ControlFlow::Continue`
/// - Abort iteration immediately (after applying the element fate) if `f(&e)`
/// returns `ControlFlow::Break`
///
/// The elements are visited in unsorted (and unspecified) order.
///
/// # Examples
///
/// ```
/// use hashbrown::HashSet;
/// use core::ops::ControlFlow;
///
/// let xs = [1,2,3,4,5,6];
/// let mut set: HashSet<i32> = xs.into_iter().collect();
/// let mut count = 0;
/// set.filter(|&k| if count < 2 {
/// if k % 2 == 0 {
/// ControlFlow::Continue(true)
/// } else {
/// ControlFlow::Continue(false)
/// }
/// } else {
/// // keep this item and break
/// ControlFlow::Break(true)
/// });
/// assert_eq!(set.len(), 3);
/// ```
pub fn filter<F>(&mut self, mut f: F)
where
F: FnMut(&T) -> core::ops::ControlFlow<bool, bool>,
{
self.map.filter(|k, _| f(k));
}

/// Drains elements which are true under the given predicate,
/// and returns an iterator over the removed items.
///
Expand Down Expand Up @@ -2980,6 +3021,30 @@ mod test_set {
assert!(set.contains(&6));
}

#[test]
fn test_filter() {
let mut set: HashSet<i32> = (0..100).collect();
// looping and removing any element > 50, but stop after 40 removals
let mut removed = 0;
set.filter(|&k| {
if k > 50 {
removed += 1;
if removed < 40 {
core::ops::ControlFlow::Continue(false)
} else {
core::ops::ControlFlow::Break(false)
}
} else {
core::ops::ControlFlow::Continue(true)
}
});
assert_eq!(set.len(), 60);
// check nothing up to 50 is removed
for k in 0..=50 {
assert!(set.contains(&k));
}
}

#[test]
fn test_extract_if() {
{
Expand Down
110 changes: 110 additions & 0 deletions src/table.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -870,6 +870,79 @@ where
}
}

/// Iterates over elements, applying the specified `ControlFlow` predicate to each
///
/// ### Element Fate
/// - Kept if `f(&e)` returns `ControlFlow::<Any>(true)`
/// - Removed if `f(&e)` returns `ControlFlow::<Any>(false)`
///
/// ### Iteration Control
/// - Continue iterating if `f(&e)` returns `ControlFlow::Continue`
/// - Abort iteration immediately (after applying the element fate) if `f(&e)`
/// returns `ControlFlow::Break`
///
/// The elements are visited in unsorted (and unspecified) order.
///
/// # Examples
///
/// ```
/// # #[cfg(feature = "nightly")]
/// # fn test() {
/// use hashbrown::{HashTable, DefaultHashBuilder};
/// use std::hash::BuildHasher;
/// use core::ops::ControlFlow;
///
/// let mut table = HashTable::new();
/// let hasher = DefaultHashBuilder::default();
/// let hasher = |val: &_| {
/// use core::hash::Hasher;
/// let mut state = hasher.build_hasher();
/// core::hash::Hash::hash(&val, &mut state);
/// state.finish()
/// };
/// let mut removed = 0;
/// for x in 1..=8 {
/// table.insert_unique(hasher(&x), x, hasher);
/// }
/// table.filter(|&mut v| if removed < 3 {
/// if v % 2 == 0 {
/// ControlFlow::Continue(true)
/// } else {
/// removed += 1;
/// ControlFlow::Continue(false)
/// }
/// } else {
/// // keep this item and break
/// ControlFlow::Break(true)
/// });
/// assert_eq!(table.len(), 5);
/// # }
/// # fn main() {
/// # #[cfg(feature = "nightly")]
/// # test()
/// # }
/// ```
pub fn filter(&mut self, mut f: impl FnMut(&mut T) -> core::ops::ControlFlow<bool, bool>) {
// Here we only use `iter` as a temporary, preventing use-after-free
unsafe {
for item in self.raw.iter() {
match f(item.as_mut()) {
core::ops::ControlFlow::Continue(kept) => {
if !kept {
self.raw.erase(item);
}
}
core::ops::ControlFlow::Break(kept) => {
if !kept {
self.raw.erase(item);
}
break;
}
}
}
}
}

/// Clears the set, returning all elements in an iterator.
///
/// # Examples
Expand Down Expand Up @@ -2372,12 +2445,49 @@ impl<T, F, A: Allocator> FusedIterator for ExtractIf<'_, T, F, A> where F: FnMut

#[cfg(test)]
mod tests {
use crate::DefaultHashBuilder;

use super::HashTable;

use core::hash::BuildHasher;
#[test]
fn test_allocation_info() {
assert_eq!(HashTable::<()>::new().allocation_size(), 0);
assert_eq!(HashTable::<u32>::new().allocation_size(), 0);
assert!(HashTable::<u32>::with_capacity(1).allocation_size() > core::mem::size_of::<u32>());
}

#[test]
fn test_filter() {
let mut table = HashTable::new();
let hasher = DefaultHashBuilder::default();
let hasher = |val: &_| {
use core::hash::Hasher;
let mut state = hasher.build_hasher();
core::hash::Hash::hash(&val, &mut state);
state.finish()
};
for x in 0..100 {
table.insert_unique(hasher(&x), x, hasher);
}
// looping and removing any value > 50, but stop after 40 removals
let mut removed = 0;
table.filter(|&mut v| {
if removed < 40 {
if v > 50 {
removed += 1;
core::ops::ControlFlow::Continue(false)
} else {
core::ops::ControlFlow::Continue(true)
}
} else {
core::ops::ControlFlow::Break(true)
}
});
assert_eq!(table.len(), 60);
// check nothing up to 50 is removed
for v in 0..=50 {
assert_eq!(table.find(hasher(&v), |&val| val == v), Some(&v));
}
}
}
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