I mean, the simple proof is that Rust has been growing by leaps and bounds in the embedded world, which is the closest to bare metal you get. It’s also being used in the Linux kernel and Windows, and there are several projects building new kernels in pure Rust. So yeah, it’s safe to say that it’s as close to the metal as C.

Also, the comparison to Java is understandable if you’ve only been exposed to Rust by the memes, but it doesn’t hold up in practice. Rust has a lot more syntax than C (although that’s not saying much), but it’s one of the most expressive languages on the market today.

My preferred variation of this is to make it an open question that leaves them in the position of authority, and assumes that they made a deliberate decision.

For example, instead of “Why aren’t you using StandardLib that does 90% of this?”, I would try “Could this be achieved with StandardLib? Seems like it would cover 90% of this”.

For anyone interested in learning more about bloom filters, this is a technical but extremely accessible and easy to follow introduction to them, including some excellent interactive visualizations: https://samwho.dev/bloom-filters/