[wip] UnalignUnsized #1828
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[wip] UnalignUnsized #1828
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joshlf
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Oct 11, 2024
src/lib.rs
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| @@ -893,6 +930,57 @@ unsafe impl<T> KnownLayout for [T] { | |||
| // struct `Foo(i32, [u8])` or `(u64, Foo)`. | |||
| slc.len() | |||
| } | |||
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| #[cfg(feature = "alloc")] | |||
| unsafe fn drop(slf: &mut UnalignUnsized<Self>) { | |||
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Does this play nicely with Pin'd types?
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Yes, Pin bars you from moving the referent before running its destructor. It doesn't place any restrictions on what you do in the destructor.
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This is achieved by adding a `MaybeUninit` associated type to `KnownLayout`, whose layout is identical to `Self` except that it admits uninitialized bytes in all positions. For sized types, this is bound to `mem::MaybeUninit<Self>`. For potentially unsized structs, we synthesize a doppelganger with the same `repr`, whose leading fields are wrapped in `mem::MaybeUninit` and whose trailing field is the `MaybeUninit` associated type of struct's original trailing field type. This type-level recursion bottoms out at `[T]`, whose `MaybeUninit` associated type is bound to `[mem::MaybeUninit<T>]`. Makes progress towards #1797
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todo!()s remain. I suspect some of this would be easier, too, if we hadPtrintegration withUnalignUnsized.