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Rollup merge of #57313 - Nemo157:box-to-pin, r=cramertj

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Improve Box<T> -> Pin<Box<T>> conversion

I found the `From` trait conversion for this very hard to find, having a named function for it is much more discoverable. Also fixes #56256 as I need that in the place I'm using this.

Has a placeholder tracking issue, will file an issue once I get feedback.
This commit is contained in:
kennytm 2019-01-05 23:56:58 +08:00 committed by GitHub
commit 676b0b0cc4
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1 changed files with 15 additions and 5 deletions
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20
src/liballoc/boxed.rs
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@ -257,6 +257,19 @@ impl<T: ?Sized> Box<T> {
{
unsafe { &mut *Box::into_raw(b) }
}
/// Converts a `Box<T>` into a `Pin<Box<T>>`
///
/// This conversion does not allocate on the heap and happens in place.
///
/// This is also available via [`From`].
#[unstable(feature = "box_into_pin", issue = "0")]
pub fn into_pin(boxed: Box<T>) -> Pin<Box<T>> {
// It's not possible to move or replace the insides of a `Pin<Box<T>>`
// when `T: !Unpin`, so it's safe to pin it directly without any
// additional requirements.
unsafe { Pin::new_unchecked(boxed) }
}
}
#[stable(feature = "rust1", since = "1.0.0")]
@ -451,15 +464,12 @@ impl<T> From<T> for Box<T> {
}
#[stable(feature = "pin", since = "1.33.0")]
impl<T> From<Box<T>> for Pin<Box<T>> {
impl<T: ?Sized> From<Box<T>> for Pin<Box<T>> {
/// Converts a `Box<T>` into a `Pin<Box<T>>`
///
/// This conversion does not allocate on the heap and happens in place.
fn from(boxed: Box<T>) -> Self {
// It's not possible to move or replace the insides of a `Pin<Box<T>>`
// when `T: !Unpin`, so it's safe to pin it directly without any
// additional requirements.
unsafe { Pin::new_unchecked(boxed) }
Box::into_pin(boxed)
}
}