Macro const_shellsort_adv 

macro_rules! const_shellsort_adv {
    ($data:expr, $cmp:path) => { ... };
    (@$seq:expr, $data:expr, $cmp:path) => { ... };
}

Sorts a const array or mutable slice as a const expression using shellsort.

The optional @ prefix parameter is the sort.

The first parameter is the data to be sorted.

The second parameter is the path identifying the macro which should be invoked to compare elements cmp!(a, b)