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Implement Unpin for Box, Rc, and Arc #53874

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Merged
merged 4 commits into from
Sep 7, 2018
Merged

Implement Unpin for Box, Rc, and Arc #53874

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c3bdd76
Implement Unpin for Box, Rc, and Arc
Aug 31, 2018
9ff29d6
Fix Rc impl.
Sep 1, 2018
c82af09
Add comment.
Sep 5, 2018
972cd8b
Fix typos.
Sep 6, 2018
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3 changes: 3 additions & 0 deletions src/liballoc/boxed.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -749,6 +749,9 @@ impl<T: ?Sized> AsMut<T> for Box<T> {
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> Unpin for Box<T> { }
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I tried looking through the issue, and it wasn't immediately clear: why is a Box unpin? After using a pin, we could move out of the box afterwards, right?

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Best summary is this comment under "adding Unpin implementations" TL;DR is you're right, but putting the box in the pin doesn't pin the stuff in the heap, only the box's stack representation (i.e. the actual pointer)

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@cramertj cramertj Sep 1, 2018 •
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Both interpretations of Box are valid, but this one is the most useful and consistent with other types (in that pin-projection is related to whether or not the data is stored out-of-line). If a Box is pinned, then there isn't a way to move the underlying data unless we choose to make it Unpin, so the other choice is fine as well.


#[unstable(feature = "generator_trait", issue = "43122")]
impl<T> Generator for Box<T>
where T: Generator + ?Sized
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5 changes: 4 additions & 1 deletion src/liballoc/rc.rs
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Expand Up @@ -252,7 +252,7 @@ use core::fmt;
use core::hash::{Hash, Hasher};
use core::intrinsics::abort;
use core::marker;
use core::marker::{Unsize, PhantomData};
use core::marker::{Unpin, Unsize, PhantomData};
use core::mem::{self, align_of_val, forget, size_of_val};
use core::ops::Deref;
use core::ops::CoerceUnsized;
Expand Down Expand Up @@ -1830,3 +1830,6 @@ impl<T: ?Sized> AsRef<T> for Rc<T> {
&**self
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> Unpin for Box<T> { }
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This looks like a copy-paste woops, it should be Rc, right? XD

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yep whoops!

5 changes: 4 additions & 1 deletion src/liballoc/sync.rs
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Expand Up @@ -27,7 +27,7 @@ use core::mem::{self, align_of_val, size_of_val};
use core::ops::Deref;
use core::ops::CoerceUnsized;
use core::ptr::{self, NonNull};
use core::marker::{Unsize, PhantomData};
use core::marker::{Unpin, Unsize, PhantomData};
use core::hash::{Hash, Hasher};
use core::{isize, usize};
use core::convert::From;
Expand Down Expand Up @@ -1942,3 +1942,6 @@ impl<T: ?Sized> AsRef<T> for Arc<T> {
&**self
}
}

#[unstable(feature = "pin", issue = "49150")]
impl<T: ?Sized> Unpin for Arc<T> { }