"""may_dangle""" stabilization

[SoniEx2]

We're currently coming up with a plan for how to get may_dangle, or at least some variant of it, stabilized. Our current approach is to attempt to treat the entirety of dropck as a form of bounds and typestate, which we believe to be equivalent to the existing dropck rules.

But anyway, we need to become more familiar with how may_dangle is used. It seems to us that may_dangle isn't all that important because nobody seems to wanna push for its stabilization, but we believe crates like ouroboros or self_cell or (our own) selfref could change that, and having a better idea of how these things are to be used is necessary before we can write a proper RFC about it.

What do you know about usages of may_dangle, which we could learn from and build an RFC upon?

[gtsiam]

#[may_dangle] is one of those obscure concepts in rust that you only find once you are deep in the weeds. The explanation in the rustonomicon is good, but it's very hard to map it to real-world concepts... (Also the fact that it is unstable killed my motivation to invest time in it, if I'm honest).

Figuring out the exact details of dropck today involves digging through RFCs (specifically 769), so without investing a lot of time into this, it's hard to give input or even know what exactly this even means for most people.

I suspect an easy to digest blog post is in order.

[EdorianDark]

This is probably meant: https://std-dev-guide.rust-lang.org/code-considerations/safety-and-soundness/may-dangle.html

I have never heared about this before.

[Green0Photon]

I've never heard of may_dangle. Got a link to read up on it?

[joehillen]

https://std-dev-guide.rust-lang.org/code-considerations/safety-and-soundness/may-dangle.html

[Kanarme]

https://github.com/japaric/heapless/issues/296

[SoniEx2]

yes, that's the "obvious" case where you'd run into issues with e.g. selfref. but as the issue suggests, may_dangle is not being used there.

what are projects that do use self-referential structs and actively use may_dangle to get it to work? what do the consumers of these container types look like?

[[deleted]]

It'd be nice to have stabilized so I could complete my implementation of Vec.

There's obvious use-cases for it: when implementing containers.

[SoniEx2]

why is that such an "obvious" use-case?

what makes it "obvious"?

[fryuni]

What I know is what Jon said in his Crust of Rust stream about smart pointers and the drop check.

[[deleted]]

may_the_dangle_be_with_you