I'd agree with you here, but Rust is powerful enough to abstract serialization behind a macro. You'd probably be using something like Serde instead of writing

I'd agree with you here, but Rust is powerful enough to abstract serialization behind a macro. You'd probably be using something like Serde instead of writing your own decoder. The macro just adds repr(C) for you and does it, if that's the design it wants to use. Rust's capabilities for abstracting in this way are still expanding, so if it can't today then it probably can tomorrow. Nonetheless, other things which aren't stable include the discriminant values of an enum and whether/if we use the null pointer optimizations. And probably others. Doing this to any Rust type is not safe as-is, and guaranteeing an ABI for all types just freezes the algorithm, as I've said elsewhere in this thread. SO I'm not seeing how this is a particular problem.