On Thu Aug 13, 2026 at 9:48 PM BST, Danilo Krummrich wrote:
> On Thu Aug 13, 2026 at 8:32 PM CEST, Yury Norov wrote:
>> pub(crate) fn alloc_area(
>> &self,
>> count: usize,
>> align: usize,
>> ) -> Result<ChannelIdArea<'_>> {
>> let count = NonZero::new(count).ok_or(EINVAL)?;
>> let align = Alignment::new_checked(align).ok_or(EINVAL)?;
>>
>> let mut ids = self.inner.lock();
>> let area = ids.find_unused_area(0, count, align).ok_or(ENOSPC)?;
>>
>> // If the pool is small, the backing bitmap may be rounded up to a
>> larger size.
>> if area.range().end > self.num_chids {
>> return Err(ENOSPC);
>> }
>>
>> Ok(ChannelIdArea {
>> pool: self,
>> range: area.acquire(),
>> })
>> }
>>
>> let area = pool.alloc_area(8, 4)?;
>>
>> See the difference? You still check the parameters, but don't make it
>> the part of interface.
>
> Miguel already replied to this, so just briefly adding to this.
>
> We usually want the arguments to already carry the invariants we require. If
> we
> make the arguments unconstrained, we may end up in situations where we already
> have types that provide certain guarantees about value constraints and yet we
> have to give up on them because the API takes unconstrained arguments and
> revalidates.
>
> The code from Eliot does actually already takes advantage of this. In
>
> pool.alloc_area(nz::<8>(), Alignment::new::<8>())?;
I have to say this looks quite ugly, compared to just `.alloc_area(8, 8)`. In
this case I'd go with something aesthetically better...
While keeping invariants with types is generally good, for primitives I'm never
a big fan of `NonZero` and `Bounded`... The turbofishes are just ugly and they
are must harder to use compared to raw primitives without typing a lot of
symbols.
Best,
Gary
>
> both arguments are already validated at compile time, whereas with
> unconstrained
> arguments we're left with a runtime check.
>
> Yes, nz() does not actually validate it statically, but it easily could (and
> probably should).
