Re: [PATCH 1/2] rust: num: casts: replace const type narrowing methods with a macro

[Danilo Krummrich]

On Tue Aug 25, 2026 at 10:25 AM CEST, Miguel Ojeda wrote:
> On Tue, Aug 25, 2026 at 4:45 AM Alexandre Courbot <acourbot@xxxxxxxxxx> wrote:
>>
>>     const DMA_LEN: u32 = casts::usize_into_u32::<{ MEM_BLOCK_ALIGNMENT }>();
>>
>> into
>>
>>     const DMA_LEN: u32 = casts::const_as!(MEM_BLOCK_ALIGNMENT => u32);
>
> Having said that, macros have a cost too when they introduce new
> "syntax", so since the beginning we have tried to minimize their use
> to where we feel is worth it.
>
> The former line above is not perfect by any means, but it is
> nevertheless syntax that one needs to already know. Personally
> speaking, I don't care if I have to write the former or the latter, to
> be honest, so I am OK with both ways.

As mentioned in [1], I also think it's not great, but I also don't mind having
it as is for now.

I guess my main question is how we expect this to evolve. How do we want this to
look like once we have things like const function arguments or const trait
methods? Is it worth getting back and forth on a macro solution with this in
mind?

[1] https://lore.kernel.org/all/DKX57FPE7DKY.1MVQBHYXKFAWT@xxxxxxxxxx/