| Returns `None` if the pointer is null, or else returns a shared reference to | |
| the value wrapped in `Some`. If the value may be uninitialized, [`as_uninit_ref`] | |
| must be used instead. If the value is known to be non-null, [`as_ref_unchecked`] | |
| can be used instead. | |
| # Safety | |
| When calling this method, you have to ensure that *either* the pointer is null *or* | |
| the pointer is [convertible to a reference](crate::ptr#pointer-to-reference-conversion). | |
| # Panics during const evaluation | |
| This method will panic during const evaluation if the pointer cannot be | |
| determined to be null or not. See [`is_null`] for more information. | |
| # Null-unchecked version | |
| If you are sure the pointer can never be null, you can use `as_ref_unchecked` which returns | |
| `&T` instead of `Option<&T>`. |