/// The `capacity` cannot exceed `isize::MAX` (only a concern on 32-bit systems).
/// If the `ptr` and `capacity` come from a `RawVec` created via `a`, then this is guaranteed.
pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, a: A) -> Self {
/// The `capacity` cannot exceed `isize::MAX` (only a concern on 32-bit systems).
/// If the `ptr` and `capacity` come from a `RawVec` created via `a`, then this is guaranteed.
pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, a: A) -> Self {