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Implement Copy and Clone for UnsafeCell<T> #55207

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Implement Copy and Clone for UnsafeCell<T> #55207

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d8951ee
Implement Copy and Clone for UnsafeCell<T>
Oct 19, 2018
4676b10
Modify stability attributes so CI can build, only impl Clone if T is …
Nov 1, 2018
67bcac6
Remove call to clone, and explain why
Nov 1, 2018
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8 changes: 3 additions & 5 deletions src/libcore/cell.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1512,16 +1512,14 @@ impl<T: ?Sized> UnsafeCell<T> {
}
}

// TODO: correct stable attribute
#[stable(feature = "rust1", since = "1.0.0")]
impl<T: Clone> Clone for UnsafeCell<T> {
#[stable(feature = "unsafe_cell_copy_clone_conservative", since = "1.31.0")]
impl<T: Clone + Copy> Clone for UnsafeCell<T> {
fn clone(&self) -> UnsafeCell<T> {
UnsafeCell::new(self.value.clone())
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This shouldn't call clone(), that is still unknown code executing.

It should make a Copy instead.

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Is there an explict way to call copy? or is this acceptable?

#[stable(feature = "unsafe_cell_copy_clone_conservative", since = "1.31.0")]
impl<T: Clone + Copy> Clone for UnsafeCell<T> {
    fn clone(&self) -> UnsafeCell<T> {
        UnsafeCell::new(self.value)
    }
}

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Yes that should do it.

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Together with a comment why we are not calling clone().

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@RalfJung impl'd in 67bcac6, thanks!

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Since Self: Copy the body of this method can even be just *self, though this is equivalent.

}
}

// TODO: correct stable attribute
#[stable(feature = "rust1", since = "1.0.0")]
#[stable(feature = "unsafe_cell_copy_clone_conservative", since = "1.31.0")]
impl<T: Copy> Copy for UnsafeCell<T> {}

#[stable(feature = "unsafe_cell_default", since = "1.10.0")]
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