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

On Tue, Aug 25, 2026 at 4:45 AM Alexandre Courbot <[email protected]> wrote:
>
>     const DMA_LEN: u32 = casts::usize_into_u32::<{ MEM_BLOCK_ALIGNMENT }>();
>
> into
>
>     const DMA_LEN: u32 = casts::const_as!(MEM_BLOCK_ALIGNMENT => u32);

Hmm... I have been following the discussion and listening to both
sides of the argument.

The macro interface looks obvious enough, and we could consider adding
it to the prelude.

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. But I worked with C++ TMP in the
past, so my eyes may be desensitized. :)

Apart from readability concerns, we are saving here a few characters;
getting possibly different codegen (forced textual inline), and maybe
having better or worse compiler-side time/memory/disk numbers. Is that
about it? It would be good to measure any actual difference.

What I wouldn't want is a raw `as`, because the point of the saga we
started a long time ago is to introduce better tools that allow us to
get rid of the almighty `as` into weaker (i.e. safer) options, even if
some uses of `as` may be "obviously right".

Cheers,
Miguel