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Auto merge of #45881 - Centril:box-leak, r=alexcrichton
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Add Box::leak<'a>(Box<T>) -> &'a mut T where T: 'a

Adds:

```rust
impl<T: ?Sized> Box<T> {
    pub fn leak<'a>(b: Box<T>) -> &'a mut T where T: 'a {
        unsafe { &mut *Box::into_raw(b) }
    }
}
```

which is useful for when you just want to put some stuff on the heap and then have a reference to it for the remainder of the program.

r? @sfackler
cc @durka
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bors committed Nov 23, 2017
2 parents 0916bbc + bc18d99 commit 246a6d1
Showing 1 changed file with 53 additions and 0 deletions.
53 changes: 53 additions & 0 deletions src/liballoc/boxed.rs
Original file line number Diff line number Diff line change
Expand Up @@ -374,6 +374,59 @@ impl<T: ?Sized> Box<T> {
unique
};
}

/// Consumes and leaks the `Box`, returning a mutable reference,
/// `&'a mut T`. Here, the lifetime `'a` may be chosen to be `'static`.
///
/// 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. If this is not acceptable, the reference should first be wrapped
/// with the [`Box::from_raw`] function producing a `Box`. This `Box` can
/// then be dropped which will properly destroy `T` and release the
/// allocated memory.
///
/// Note: this is an associated function, which means that you have
/// to call it as `Box::leak(b)` instead of `b.leak()`. This
/// is so that there is no conflict with a method on the inner type.
///
/// [`Box::from_raw`]: struct.Box.html#method.from_raw
///
/// # Examples
///
/// Simple usage:
///
/// ```
/// #![feature(box_leak)]
///
/// fn main() {
/// let x = Box::new(41);
/// let static_ref: &'static mut usize = Box::leak(x);
/// *static_ref += 1;
/// assert_eq!(*static_ref, 42);
/// }
/// ```
///
/// Unsized data:
///
/// ```
/// #![feature(box_leak)]
///
/// fn main() {
/// let x = vec![1, 2, 3].into_boxed_slice();
/// let static_ref = Box::leak(x);
/// static_ref[0] = 4;
/// assert_eq!(*static_ref, [4, 2, 3]);
/// }
/// ```
#[unstable(feature = "box_leak", reason = "needs an FCP to stabilize",
issue = "46179")]
#[inline]
pub fn leak<'a>(b: Box<T>) -> &'a mut T
where
T: 'a // Technically not needed, but kept to be explicit.
{
unsafe { &mut *Box::into_raw(b) }
}
}

#[stable(feature = "rust1", since = "1.0.0")]
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