ZST alignment | Rust Programming Language Community | Page 1

worthy knot Feb 17, 2023, 7:46 AM

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Just reading nomicon a bit and reading about handling ZSTs it seemed to imply that although ptr::read is a no-op for ZST the pointer should still be aligned, and that if just blindly incrementing the pointer by 1 each time it might not be aligned.

However I always assumed ZSTs would be guaranteed to have an alignment of 1 (minimal alignment) so incrementing pointer address each time by 1 wouldn't be able to misalign it.

Is it correct that we can't guarantee ZSTs have an alignment of 1 then?, or is the author being overly cautious there?.

mellow saddle Feb 17, 2023, 8:28 AM

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worthy knot Just reading nomicon a bit and reading about handling ZSTs it seemed to imply th...

?eval std::mem::align_of::<[usize; 0]>()

jovial aspenBOT Feb 17, 2023, 8:28 AM

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     Running `target/debug/playground`

8

mellow saddle Feb 17, 2023, 8:29 AM

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"normal" ZSTs have align 1

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(), struct Foo;, struct Bar(Foo, (), Foo);

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however you can set the align with #[align(N)], and for example arrays have align of the element

#ZST alignment