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Merged
Gankra merged 1 commit into from
Dec 5, 2022
Merged

Add splice to thin_vec #41

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309 changes: 251 additions & 58 deletions src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1438,6 +1438,53 @@ impl<T> ThinVec<T> {
}
}

/// Creates a splicing iterator that replaces the specified range in the vector
/// with the given `replace_with` iterator and yields the removed items.
/// `replace_with` does not need to be the same length as `range`.
///
/// `range` is removed even if the iterator is not consumed until the end.
///
/// It is unspecified how many elements are removed from the vector
/// if the `Splice` value is leaked.
///
/// The input iterator `replace_with` is only consumed when the `Splice` value is dropped.
///
/// This is optimal if:
///
/// * The tail (elements in the vector after `range`) is empty,
/// * or `replace_with` yields fewer or equal elements than `range`’s length
/// * or the lower bound of its `size_hint()` is exact.
///
/// Otherwise, a temporary vector is allocated and the tail is moved twice.
///
/// # Panics
///
/// Panics if the starting point is greater than the end point or if
/// the end point is greater than the length of the vector.
///
/// # Examples
///
/// ```
/// use thin_vec::{ThinVec, thin_vec};
///
/// let mut v = thin_vec![1, 2, 3, 4];
/// let new = [7, 8, 9];
/// let u: ThinVec<_> = v.splice(1..3, new).collect();
/// assert_eq!(v, &[1, 7, 8, 9, 4]);
/// assert_eq!(u, &[2, 3]);
/// ```
#[inline]
pub fn splice<R, I>(&mut self, range: R, replace_with: I) -> Splice<'_, I::IntoIter>
where
R: RangeBounds<usize>,
I: IntoIterator<Item = T>,
{
Splice {
drain: self.drain(range),
replace_with: replace_with.into_iter(),
}
}

/// Resize the buffer and update its capacity, without changing the length.
/// Unsafe because it can cause length to be greater than capacity.
unsafe fn reallocate(&mut self, new_cap: usize) {
Expand Down Expand Up @@ -2412,6 +2459,133 @@ impl<'a, T> AsRef<[T]> for Drain<'a, T> {
}
}

/// A splicing iterator for `ThinVec`.
///
/// This struct is created by [`ThinVec::splice`][].
/// See its documentation for more.
///
/// # Example
///
/// ```
/// use thin_vec::thin_vec;
///
/// let mut v = thin_vec![0, 1, 2];
/// let new = [7, 8];
/// let iter: thin_vec::Splice<_> = v.splice(1.., new);
/// ```
#[derive(Debug)]
pub struct Splice<'a, I: Iterator + 'a> {
drain: Drain<'a, I::Item>,
replace_with: I,
}

impl<I: Iterator> Iterator for Splice<'_, I> {
type Item = I::Item;

fn next(&mut self) -> Option<Self::Item> {
self.drain.next()
}

fn size_hint(&self) -> (usize, Option<usize>) {
self.drain.size_hint()
}
}

impl<I: Iterator> DoubleEndedIterator for Splice<'_, I> {
fn next_back(&mut self) -> Option<Self::Item> {
self.drain.next_back()
}
}

impl<I: Iterator> ExactSizeIterator for Splice<'_, I> {}

impl<I: Iterator> Drop for Splice<'_, I> {
fn drop(&mut self) {
// Ensure we've fully drained out the range
self.drain.by_ref().for_each(drop);

unsafe {
// If there's no tail elements, then the inner ThinVec is already
// correct and we can just extend it like normal.
if self.drain.tail == 0 {
(*self.drain.vec).extend(self.replace_with.by_ref());
return;
}

// First fill the range left by drain().
if !self.drain.fill(&mut self.replace_with) {
return;
}

// There may be more elements. Use the lower bound as an estimate.
let (lower_bound, _upper_bound) = self.replace_with.size_hint();
if lower_bound > 0 {
self.drain.move_tail(lower_bound);
if !self.drain.fill(&mut self.replace_with) {
return;
}
}

// Collect any remaining elements.
// This is a zero-length vector which does not allocate if `lower_bound` was exact.
let mut collected = self
.replace_with
.by_ref()
.collect::<Vec<I::Item>>()
.into_iter();
// Now we have an exact count.
if collected.len() > 0 {
self.drain.move_tail(collected.len());
let filled = self.drain.fill(&mut collected);
debug_assert!(filled);
debug_assert_eq!(collected.len(), 0);
}
}
// Let `Drain::drop` move the tail back if necessary and restore `vec.len`.
}
}

/// Private helper methods for `Splice::drop`
impl<T> Drain<'_, T> {
/// The range from `self.vec.len` to `self.tail_start` contains elements
/// that have been moved out.
/// Fill that range as much as possible with new elements from the `replace_with` iterator.
/// Returns `true` if we filled the entire range. (`replace_with.next()` didn’t return `None`.)
unsafe fn fill<I: Iterator<Item = T>>(&mut self, replace_with: &mut I) -> bool {
let vec = unsafe { &mut *self.vec };
let range_start = vec.len();
let range_end = self.end;
let range_slice = unsafe {
slice::from_raw_parts_mut(vec.data_raw().add(range_start), range_end - range_start)
};

for place in range_slice {
if let Some(new_item) = replace_with.next() {
unsafe { ptr::write(place, new_item) };
vec.set_len(vec.len() + 1);
} else {
return false;
}
}
true
}

/// Makes room for inserting more elements before the tail.
unsafe fn move_tail(&mut self, additional: usize) {
let vec = unsafe { &mut *self.vec };
let len = self.end + self.tail;
vec.reserve(len.checked_add(additional).expect("capacity overflow"));

let new_tail_start = self.end + additional;
unsafe {
let src = vec.data_raw().add(self.end);
let dst = vec.data_raw().add(new_tail_start);
ptr::copy(src, dst, self.tail);
}
self.end = new_tail_start;
}
}

/// Write is implemented for `ThinVec<u8>` by appending to the vector.
/// The vector will grow as needed.
/// This implementation is identical to the one for `Vec<u8>`.
Expand Down Expand Up @@ -2648,6 +2822,19 @@ mod tests {
assert_eq!(&v[..], &[]);
}

{
let mut v = ThinVec::<i32>::new();
assert_eq!(v.splice(.., []).len(), 0);

for _ in v.splice(.., []) {
unreachable!()
}

assert_eq!(v.len(), 0);
assert_eq!(v.capacity(), 0);
assert_eq!(&v[..], &[]);
}

{
let mut v = ThinVec::<i32>::new();
v.truncate(1);
Expand Down Expand Up @@ -3402,70 +3589,76 @@ mod std_tests {
v.drain(5..=5);
}

/* TODO: implement splice?
#[test]
fn test_splice() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
v.splice(2..4, a.iter().cloned());
assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
v.splice(1..3, Some(20));
assert_eq!(v, &[1, 20, 11, 12, 5]);
}
#[test]
fn test_splice() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
v.splice(2..4, a.iter().cloned());
assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
v.splice(1..3, Some(20));
assert_eq!(v, &[1, 20, 11, 12, 5]);
}

#[test]
fn test_splice_inclusive_range() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
let t1: ThinVec<_> = v.splice(2..=3, a.iter().cloned()).collect();
assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
assert_eq!(t1, &[3, 4]);
let t2: ThinVec<_> = v.splice(1..=2, Some(20)).collect();
assert_eq!(v, &[1, 20, 11, 12, 5]);
assert_eq!(t2, &[2, 10]);
}
#[test]
fn test_splice_inclusive_range() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
let t1: ThinVec<_> = v.splice(2..=3, a.iter().cloned()).collect();
assert_eq!(v, &[1, 2, 10, 11, 12, 5]);
assert_eq!(t1, &[3, 4]);
let t2: ThinVec<_> = v.splice(1..=2, Some(20)).collect();
assert_eq!(v, &[1, 20, 11, 12, 5]);
assert_eq!(t2, &[2, 10]);
}

#[test]
#[should_panic]
fn test_splice_out_of_bounds() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
v.splice(5..6, a.iter().cloned());
}
#[test]
#[should_panic]
fn test_splice_out_of_bounds() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
v.splice(5..6, a.iter().cloned());
}

#[test]
#[should_panic]
fn test_splice_inclusive_out_of_bounds() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
v.splice(5..=5, a.iter().cloned());
}
#[test]
#[should_panic]
fn test_splice_inclusive_out_of_bounds() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
v.splice(5..=5, a.iter().cloned());
}

#[test]
fn test_splice_items_zero_sized() {
let mut vec = thin_vec![(), (), ()];
let vec2 = thin_vec![];
let t: ThinVec<_> = vec.splice(1..2, vec2.iter().cloned()).collect();
assert_eq!(vec, &[(), ()]);
assert_eq!(t, &[()]);
}
#[test]
fn test_splice_items_zero_sized() {
let mut vec = thin_vec![(), (), ()];
let vec2 = thin_vec![];
let t: ThinVec<_> = vec.splice(1..2, vec2.iter().cloned()).collect();
assert_eq!(vec, &[(), ()]);
assert_eq!(t, &[()]);
}

#[test]
fn test_splice_unbounded() {
let mut vec = thin_vec![1, 2, 3, 4, 5];
let t: ThinVec<_> = vec.splice(.., None).collect();
assert_eq!(vec, &[]);
assert_eq!(t, &[1, 2, 3, 4, 5]);
}
#[test]
fn test_splice_unbounded() {
let mut vec = thin_vec![1, 2, 3, 4, 5];
let t: ThinVec<_> = vec.splice(.., None).collect();
assert_eq!(vec, &[]);
assert_eq!(t, &[1, 2, 3, 4, 5]);
}

#[test]
fn test_splice_forget() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
::std::mem::forget(v.splice(2..4, a.iter().cloned()));
assert_eq!(v, &[1, 2]);
}
*/
#[test]
fn test_splice_forget() {
let mut v = thin_vec![1, 2, 3, 4, 5];
let a = [10, 11, 12];
::std::mem::forget(v.splice(2..4, a.iter().cloned()));
assert_eq!(v, &[1, 2]);
}

#[test]
fn test_splice_from_empty() {
let mut v = thin_vec![];
let a = [10, 11, 12];
v.splice(.., a.iter().cloned());
assert_eq!(v, &[10, 11, 12]);
}

/* probs won't ever impl this
#[test]
Expand Down