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Add excess capacity description for Vec::leak #79257

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Add excess capacity description for Vec::leak #79257

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596d1f2
Add excess capacity description on Vec::leak
Nov 21, 2020
747e8ff
Fix example
Dec 2, 2020
b2d873f
Fix build error
Feb 7, 2021
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14 changes: 14 additions & 0 deletions library/alloc/src/vec/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1783,6 +1783,20 @@ impl<T, A: Allocator> Vec<T, A> {
/// static_ref[0] += 1;
/// assert_eq!(static_ref, &[2, 2, 3]);
/// ```
///
/// Drop excess capacity:
///
/// ```
/// let mut v = Vec::with_capacity(10);
/// v.extend([1, 2, 3].iter().cloned());
/// let slice = v.clone().into_boxed_slice();
///
/// unsafe {
/// let p = slice.as_ptr();
/// let rebuilt = std::slice::from_raw_parts(p, slice.len());
/// assert_eq!(rebuilt.len(), 3);
/// }
Comment on lines +1790 to +1798
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This example doesn't demonstrate any leaking. .into_boxed_slice() returns a Box, which the slice variable will own.

The issue this PR was originally trying to fix is that the documentation doesn't promise this function drops excess capacity. However, I don't think that's something we want to fix. Instead, I think it'd be better if leak explicitly does not drop the excess capacity. But for that, there's an RFC which has been standing still for a while: rust-lang/rfcs#2969

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@m-ou-se Thank you for your support and help. I've been stucking and would like to close my PR.

/// ```
#[stable(feature = "vec_leak", since = "1.47.0")]
#[inline]
pub fn leak<'a>(self) -> &'a mut [T]
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