alt Hacker News> I've been doing low-level programming professionally for 25 years
You haven't been doing any Rust though. You seem to think you can extrapolate your C++ experience to Rust. That's preposterous. The actual Rust programmers can't recognize this theoretical problem in their Rust programs.
Could that be because the language is fairly young? You don't see the "20-year-old legacy system" in Rust because it doesn't exist yet ;)
And if you look at other comments in this thread, many engineers have this mentality of "just use a crate, it's probably optimised already". They might not have performance problems immediately or obviously but it's more like ten thousand papercuts - a few allocations here and there, a few extra copies here and there and you've got a way slower program than it should have been.