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(#102929) Implement String:leak #102941

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(#102929) Implement String:leak #102941

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248a9f4
impl String:leak.
finnbear Oct 12, 2022
4ee922a
Add feature so doctest works.
finnbear Oct 12, 2022
78eaa5e
Move feature to doc comment.
finnbear Oct 12, 2022
3e882e2
Revisions.
finnbear Oct 18, 2022
687dd3d
Allow if no_global_oom_handling, like `Vec::leak`.
finnbear Oct 19, 2022
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30 changes: 29 additions & 1 deletion library/alloc/src/string.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,7 +69,7 @@ use crate::boxed::Box;
use crate::collections::TryReserveError;
use crate::str::{self, Chars, Utf8Error};
#[cfg(not(no_global_oom_handling))]
use crate::str::{from_boxed_utf8_unchecked, FromStr};
use crate::str::{from_boxed_utf8_unchecked, from_utf8_unchecked_mut, FromStr};
use crate::vec::Vec;

/// A UTF-8–encoded, growable string.
Expand Down Expand Up @@ -1849,6 +1849,34 @@ impl String {
let slice = self.vec.into_boxed_slice();
unsafe { from_boxed_utf8_unchecked(slice) }
}

/// Consumes and leaks the `String`, returning a mutable reference to the contents,
/// `&'a mut str`.
///
/// This function is mainly useful for data that lives for the remainder of
/// the program's life. Dropping the returned reference will cause a memory
/// leak.
///
/// # Examples
///
/// Simple usage:
///
/// ```
/// #![feature(string_leak)]
///
/// pub fn main() {
/// let x = String::from("bucket");
/// let static_ref: &'static mut str = x.leak();
/// assert_eq!(static_ref, "bucket");
/// }
/// ```
#[cfg(not(no_global_oom_handling))]
#[unstable(feature = "string_leak", issue = "102929")]
#[inline]
pub fn leak<'a>(self) -> &'a mut str {
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Is there any reason to use a generic <'a> instead of just 'static here? I believe the only reason we use <'a> for Vec<T> is for situations where T: !'static.

Suggested change
pub fn leak<'a>(self) -> &'a mut str {
pub fn leak(self) -> &'static mut str {

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Good idea; as I understand it, variance will still allow the 'static to be used for any 'a

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Actually, I think there is another reason. Vec is generic over A: Allocator and this may apply to String in the future. At that point, the generic lifetime would be bounded by that of the allocator. I don't know if adding the generic lifetime later would be a breaking change. Thoughts?

image
image

let slice = self.into_bytes().leak();
unsafe { from_utf8_unchecked_mut(slice) }
}
}

impl FromUtf8Error {
Expand Down