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Lokathor / bytemuck

A crate for mucking around with piles of bytes
https://docs.rs/bytemuck
Apache License 2.0
697 stars 77 forks source link

no-uninit trait with interior mutability #218

Open m-mueller678 opened 8 months ago

m-mueller678 commented 8 months ago

I would like a marker trait that enforces only the must not contain any uninit (or padding) bytes requirement. In particular, it should allow interior mutability. While I cannot think of any safe functions bytemuck could implement just with those guarantees, it is still a nice invariant to have. I am currently implementing multiple types that need this and am manually checking that there is no padding in there. Having it automatically checked via a derive macro similar to Uninit would be much less error-prone. Bytemuck seems like a natural place to put this, as it has other memory-related marker traits and there is probably a lot of overlap in the proc-macro functionality.

Lokathor commented 8 months ago

Doesn't NoUninit have a derive already?

m-mueller678 commented 8 months ago

It does, but it does not permit interior mutability. I'm looking for a more relaxed version of NoUninit

Lokathor commented 8 months ago

Ah, right.

Well then as you say, I'm not sure what operation such a trait allows, since the interior mutability part makes most things probably not work quite right.

m-mueller678 commented 8 months ago

I don't think this alone allows you to implement any useful operations. It just offloads some of the work of manual checking onto the type system. I definitely want a trait like that, but making a new crate just for this one marker trait feels overkill. So I thought, bytemuck would be a good place to put it.

Lokathor commented 8 months ago

If it doesn't allow at least one operation I'm unclear why you'd want to put the info in the type system though.

m-mueller678 commented 8 months ago

I use it as a bound on traits that have additional requirements which must be checked manually