Consider Boxed Slices

[danakj]

Box<SliceMut<T>> could own the pointer in SliceMut (like Box<[T]> in Rust).

The advantage over Vec is really you don't have a capacity field anymore.

We'd need Vec::into_boxed_slice, Box<SliceMut<T>::from(Vec<T>), Box<SliceMut<T>::from_iter(IntoIterator<T> auto)