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The original was posted on /r/rust by /u/wyf0 on 2025-12-20 14:52:43+00:00.

Hi Rust,

The intern I am supervising wanted to have dynamic asynchronous callbacks in a no_std, no-alloc environment. After a bunch of back-and-forths, punctuated by many “unsafe code is hard” exclamations, we came up with a prototype that feels good enough.

I’ve published it at https://github.com/wyfo/dyn-fn. Miri didn’t find any issues, but it still has a lot of unsafe code, so I can’t guarantee that it is perfectly sound. Any sharp eye willing to review it is welcome.

As it is still experimental, it is not yet published on crates.io. I’m tempted to go further and generalize the idea to arbitrary async traits, so stay tuned.