Re: [PATCH v5 21/38] rust: ptr: add const_align_up() and enable inline_const feature

["Gary Guo" <gary@garyguo.net>]

On Thu Mar 5, 2026 at 1:59 PM GMT, Alexandre Courbot wrote:
> On Thu Mar 5, 2026 at 9:28 PM JST, Gary Guo wrote:
>>>
>>>   const TEST_ALIGN: usize = const_align_up::<256, 10>();
>>>
>>> This uses purely const asserts, but you have to work with two `usize`
>>> arguments. The version below looks a bit nicer as it leverages the
>>> power-of-two invariant of `Alignment`:
>>>
>>>   impl Alignment {
>>>       const fn const_align_up(self, value: usize) -> usize {
>>>           build_assert!(value <= usize::MAX - !self.mask());
>>>
>>>           (value + !self.mask()) & self.mask()
>>>       }
>>
>> This is fine, too, although I think just returning an `Option` and ask user to
>> unwrap it in const eval is better.
>
> Why? Aren't unwraps something we want to avoid?
>
> We already have fallible methods for non-const contexts, so why give
> another method that essentially behaves the same when we want to use it
> in scenarios where we know the result will be successful anyway?

Unwrap is only bad when it can panic. It's not an issue for things that is
apparently const eval only, e.g. inside `const {}` or `const FOO: Bar = baz`.

Best,
Gary