Looks good to me except for the addition of the format! calls. I think those are new memory allocations that we didn't have with write!. And all of them are just for surrounding a value with fixed strings. Could you replace each format! call with a sequence of three calls to extend?

It looks like all of the format! calls are actually formatting integers, so I'm not sure of a way to avoid format! or .to_string() on those.

Oh I missed that.

I think one option would be to use the itoa crate for that. It seems to be a very lightweight dependency. What do you think?

itoa looks nice! I’ll add that in.

All set, I replaced integer formatting with itoa, and single-character extends with push.

Also, I was able to avoid allocations for nested serialize calls by simply calling self.serialize(val) rather than self.w.extend(serialize(val).as_bytes()).

Excellent, thank you!

Released as 0.11.0.

Out of curiosity, what's your use case for running this in a no_std context?

For my objdiff tool, I've been working on ensuring all dependencies are #![no_std] for the core layer that can compile to WASM. Specifically for reduced binary size and control over WASI imports.