A functional take on generating a span over an entire byte string

functional.rs

/// Computes the flux over the provided input byte string.
fn flux_over_byte_string<T>(input: T) -> Option<Flux>
where
    T: AsRef<[u8]> {
    input.as_ref()
        .iter()
        .cloned()
        .map(Flux::from)
        .fold(None, |acc, next| span_opt(acc, Some(next)))
}