[PATCH v5 04/23] rust: add new `num` module with `PowerOfTwo` type

[Alexandre Courbot]

On Sun Jun 15, 2025 at 2:31 AM JST, Boqun Feng wrote:
> On Thu, Jun 12, 2025 at 11:01:32PM +0900, Alexandre Courbot wrote:
> [...]
>> +/// An unsigned integer which is guaranteed to be a power of 2.
>> +#[derive(Debug, Clone, Copy)]
>> +#[repr(transparent)]
>> +pub struct PowerOfTwo<T>(T);
>> +
> [...]
>> +impl<T> Deref for PowerOfTwo<T> {
>
> Why do we need `impl Deref` (and the `impl Borrow` below)? A similar
> concept `NonZero` in std doesn't impl them as well.

I wanted to be exhaustive but you're right, we don't really need these
implementations (especially if `NonZero` doesn't provide them either).

>
>> +    type Target = T;
>> +
>> +    fn deref(&self) -> &Self::Target {
>> +        &self.0
>> +    }
>> +}
>> +
>> +impl<T> PartialEq for PowerOfTwo<T>
>
> Any reason you want to impl these manually instead of deriving? For
> `NonZero`, the std wants to impl these traits only for
> `ZeroablePrimitive` types, but we don't have a similar trait here.

Deriving works perfectly well! :) Thanks for pointing this out.