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Speed up Vec::clear(). #95664

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Speed up Vec::clear(). #95664

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13 changes: 12 additions & 1 deletion library/alloc/src/vec/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1881,7 +1881,18 @@ impl<T, A: Allocator> Vec<T, A> {
#[inline]
#[stable(feature = "rust1", since = "1.0.0")]
pub fn clear(&mut self) {
self.truncate(0)
let elems: *mut [T] = self.as_mut_slice();

// SAFETY:
// - `elems` comes directly from `as_mut_slice` and is therefore valid.
// - Setting `self.len` before calling `drop_in_place` means that,
// if an element's `Drop` impl panics, the vector's `Drop` impl will
// do nothing (leaking the rest of the elements) instead of dropping
// some twice.
unsafe {
self.len = 0;
ptr::drop_in_place(elems);
}
}

/// Returns the number of elements in the vector, also referred to
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