Re: [PATCH 1/5] rust: ptr: add panicking index projection variant

[Gary Guo]

On Mon Apr 27, 2026 at 12:24 PM BST, Andreas Hindborg wrote:
>> +
>> +    #[inline(always)]
>> +    fn index(self, slice: *mut [T]) -> *mut T {
>> +        // Leverage Rust built-in operators for bounds checking.
>> +        // SAFETY: All non-null and aligned pointers are valid for ZST read.
>> +        unsafe { core::slice::from_raw_parts::<()>(core::ptr::dangling(), slice.len())[self] };
>
> I think this would be more readable if you move the indexing operation
> out of the unsafe block:
>
>         // SAFETY: All non-null and aligned pointers are valid for ZST read.
>         let slice = unsafe { core::slice::from_raw_parts::<()>(core::ptr::dangling(), slice.len()) };
>         // Leverage Rust built-in operators for bounds checking.
>         slice[self];
>
>> +        slice.cast::<T>().wrapping_add(self)
>> +    }
>>  }
>>
>>  // SAFETY: `get`-returned pointer has the same provenance as `slice` and the offset is checked to
>> @@ -100,6 +116,18 @@ fn get(self, slice: *mut [T]) -> Option<*mut [T]> {
>>              new_len,
>>          ))
>>      }
>> +
>> +    #[inline(always)]
>> +    fn index(self, slice: *mut [T]) -> *mut [T] {
>> +        // Leverage Rust built-in operators for bounds checking.
>> +        // SAFETY: All non-null and aligned pointers are valid for ZST read.
>> +        unsafe {
>> +            _ = core::slice::from_raw_parts::<()>(core::ptr::dangling(), slice.len())[self.clone()];
>
> Same comment regarding moving indexing to next line.
>
> Side question: Why do you need to explicitly discard the return value
> here (`_ = ...`) and not above?

Because the result of indexing is a slice, which is unsized.

Best,
Gary

>
>
> Reviewed-by: Andreas Hindborg <a.hindborg@xxxxxxxxxx>
>
>
> Best regards,
> Andreas Hindborg