[pointer] Fix Ptr[Inner] variance #2351
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joshlf
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Feb 18, 2025
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Previously, `Ptr<'a, T>` and `PtrInner<'a, T>` documented themselves to be covariant in both `'a` and `T`. This was true for `PtrInner`, but not for `Ptr`, which used GATs, which are invariant. This is also not the desired variance: for `Exclusive` aliasing, the desired variance matches that of `&mut` references - namely, covariant in `'a` but invariant in `T`. This commit fixes this by making `Ptr<'a, T>` and `PtrInner<'a, T>` unconditionally covariant in `'a` and invariant in `T`. gherrit-pr-id: I29f8429d9d7b14026313f030f8dc1e895a98ad56
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joshlf
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Feb 18, 2025
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Previously, `Ptr<'a, T>` and `PtrInner<'a, T>` documented themselves to be covariant in both `'a` and `T`. This was true for `PtrInner`, but not for `Ptr`, which used GATs, which are invariant. This is also not the desired variance: for `Exclusive` aliasing, the desired variance matches that of `&mut` references - namely, covariant in `'a` but invariant in `T`. This commit fixes this by making `Ptr<'a, T>` and `PtrInner<'a, T>` unconditionally covariant in `'a` and invariant in `T`. gherrit-pr-id: I29f8429d9d7b14026313f030f8dc1e895a98ad56
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Backporting in #2393 |
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Previously, `Ptr<'a, T>` and `PtrInner<'a, T>` documented themselves to be covariant in both `'a` and `T`. This was true for `PtrInner`, but not for `Ptr`, which used GATs, which are invariant. This is also not the desired variance: for `Exclusive` aliasing, the desired variance matches that of `&mut` references - namely, covariant in `'a` but invariant in `T`. This commit fixes this by making `Ptr<'a, T>` and `PtrInner<'a, T>` unconditionally covariant in `'a` and invariant in `T`. gherrit-pr-id: I29f8429d9d7b14026313f030f8dc1e895a98ad56
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Previously, `Ptr<'a, T>` and `PtrInner<'a, T>` documented themselves to be covariant in both `'a` and `T`. This was true for `PtrInner`, but not for `Ptr`, which used GATs, which are invariant. This is also not the desired variance: for `Exclusive` aliasing, the desired variance matches that of `&mut` references - namely, covariant in `'a` but invariant in `T`. This commit fixes this by making `Ptr<'a, T>` and `PtrInner<'a, T>` unconditionally covariant in `'a` and invariant in `T`. gherrit-pr-id: I29f8429d9d7b14026313f030f8dc1e895a98ad56
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Previously,
Ptr<'a, T>andPtrInner<'a, T>documented themselves tobe covariant in both
'aandT. This was true forPtrInner, but notfor
Ptr, which used GATs, which are invariant. This is also not thedesired variance: for
Exclusivealiasing, the desired variance matchesthat of
&mutreferences - namely, covariant in'abut invariant inT.This commit fixes this by making
Ptr<'a, T>andPtrInner<'a, T>unconditionally covariant in
'aand invariant inT.This PR is on branch transmute-from.