Function cycle_sort_by_key 

pub fn cycle_sort_by_key<T, F, U>(slice: &mut [T], key: &F) -> usize
where
    F: Fn(&T) -> U,
    U: Ord,

Sorts a slice with a key extraction function and returns the number of writes made.

Examples

// sort by length
let mut a = ["zwölf", "zzxjoanw", "zymbel"];
let     w = cycle_sort_by_key(&mut a, &|s| s.len());

assert_eq!(a, ["zwölf", "zymbel", "zzxjoanw"]);
assert_eq!(w, 2);