I mistakenly assumed that choose_multiple functions like Python's random.choices, which performs sampling with replacement. This led to unexpected behaviour in the following Rust code:

let sample =  5..20.choose_multiple(&mut rng, my_vec.len())

Here, my_vec contains significantly more than 15 elements, but sample ends up with only 15 elements. This behaviour can be surprising and may introduce bugs.

Since choose_multiple performs sampling without replacement, it would make more sense for it to return a Result or Option to return error or None when the requested number of elements cannot be selected without replacement.