Function map_slice_box_in_place 

pub fn map_slice_box_in_place<A, B, F>(values: Box<[A]>, map: F) -> Box<[B]>
where
    A: ArrayCast,
    B: ArrayCast<Array = <A as ArrayCast>::Array>,
    F: FnMut(A) -> B,

Available on crate feature alloc only.

Map values of color A to values of color B without creating a new Box<[B]>.

This uses the guarantees of ArrayCast to reuse the allocation.