Function maligned::align_first_boxed

#[must_use]pub fn align_first_boxed<T, A: Alignment, F: FnMut(usize) -> T>(
    s_capacity: usize, 
    f: F
) -> Box<[T]>

Aligns types and initializes memory to the return value provided by the closure. Since boxed slices can never re-allocate the first item will always be aligned.

let f = |i|(i & u8::max_value() as usize) as u8;
let s = align_first_boxed::<u8, A128, _>(1023, f);
assert_eq!(s.len(), 1023);
s.iter().for_each(|b| assert_eq!(*b, f(*b as usize)));