>> It runs about five times slower than the equivalent program
> I'd be interested in hearing more about how these were benchmarked. On my machine, they both run in roughly the same time, with a degree of variance that makes them roughly equivalent. Some runs, the iterator version is faster.
It's common to forget to turn on optimizations, which _seriously_ impact Rust's runtimes, LLVM can do wonders here. Generally speaking, if iterators are slower than a loop, that's a bug.
In my novice benchmark I found similar results as OP.
running 6 tests
test for_range_100 ... bench: 89 ns/iter (+/- 2)
test for_range_1000 ... bench: 929 ns/iter (+/- 98)
test for_range_10000 ... bench: 8815 ns/iter (+/- 414)
test for_while_100 ... bench: 36 ns/iter (+/- 3)
test for_while_1000 ... bench: 294 ns/iter (+/- 27)
test for_while_10000 ... bench: 2768 ns/iter (+/- 268)
test result: ok. 0 passed; 0 failed; 0 ignored; 6 measured