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93 lines
3.1 KiB
Rust
93 lines
3.1 KiB
Rust
//! This is a copy-paste of `Vec::extract_if` for `ThinVec`.
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//!
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//! FIXME: <https://github.com/Gankra/thin-vec/pull/66> is merged, this can be removed.
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use std::{ptr, slice};
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use thin_vec::ThinVec;
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/// An iterator for [`ThinVec`] which uses a closure to determine if an element should be removed.
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#[must_use = "iterators are lazy and do nothing unless consumed"]
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pub struct ExtractIf<'a, T, F> {
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vec: &'a mut ThinVec<T>,
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/// The index of the item that will be inspected by the next call to `next`.
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idx: usize,
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/// The number of items that have been drained (removed) thus far.
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del: usize,
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/// The original length of `vec` prior to draining.
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old_len: usize,
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/// The filter test predicate.
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pred: F,
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}
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impl<'a, T, F> ExtractIf<'a, T, F>
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where
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F: FnMut(&mut T) -> bool,
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{
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pub fn new(vec: &'a mut ThinVec<T>, filter: F) -> Self {
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let old_len = vec.len();
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// Guard against us getting leaked (leak amplification)
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unsafe {
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vec.set_len(0);
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}
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ExtractIf { vec, idx: 0, del: 0, old_len, pred: filter }
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}
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}
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impl<T, F> Iterator for ExtractIf<'_, T, F>
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where
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F: FnMut(&mut T) -> bool,
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{
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type Item = T;
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fn next(&mut self) -> Option<Self::Item> {
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unsafe {
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while self.idx < self.old_len {
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let i = self.idx;
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let v = slice::from_raw_parts_mut(self.vec.as_mut_ptr(), self.old_len);
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let drained = (self.pred)(&mut v[i]);
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// Update the index *after* the predicate is called. If the index
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// is updated prior and the predicate panics, the element at this
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// index would be leaked.
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self.idx += 1;
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if drained {
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self.del += 1;
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return Some(ptr::read(&v[i]));
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} else if self.del > 0 {
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let del = self.del;
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let src: *const T = &v[i];
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let dst: *mut T = &mut v[i - del];
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ptr::copy_nonoverlapping(src, dst, 1);
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}
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}
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None
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}
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}
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fn size_hint(&self) -> (usize, Option<usize>) {
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(0, Some(self.old_len - self.idx))
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}
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}
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impl<A, F> Drop for ExtractIf<'_, A, F> {
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fn drop(&mut self) {
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unsafe {
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if self.idx < self.old_len && self.del > 0 {
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// This is a pretty messed up state, and there isn't really an
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// obviously right thing to do. We don't want to keep trying
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// to execute `pred`, so we just backshift all the unprocessed
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// elements and tell the vec that they still exist. The backshift
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// is required to prevent a double-drop of the last successfully
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// drained item prior to a panic in the predicate.
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let ptr = self.vec.as_mut_ptr();
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let src = ptr.add(self.idx);
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let dst = src.sub(self.del);
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let tail_len = self.old_len - self.idx;
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src.copy_to(dst, tail_len);
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}
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self.vec.set_len(self.old_len - self.del);
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}
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}
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}
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