[array_key_first]

I agree, but the converse is also true and is where the value of this DARPA grant lies:

There's a lot of legacy C code that people want to expand on today, but they can't because the existing program is in C and they don't want to write more potentially unsafe C code or add onto an already iffy system.

If we can rewrite in Rust, we can get safety, which is cool but not the main draw. The main draw, I think, is you now have a rust codebase, and you can continue on with that.