On Sat, Feb 5, 2022 at 10:38 AM Marcelo Cantos <marcelo.can...@gmail.com> wrote:
>
> I am porting an int-set type to generics. It holds bits in a block structure
> with 512 bits per block. At some point, I need to divide by 512:
>
> func block[T constraints.Integer](i T) T {
> return i / 512
> }
>
> Go 1.18 beta 2 complains: cannot convert 512 (untyped int constant) to T
>
> The problem is that uint8 and int8 cannot represent the number 512. If I
> build a constraint similar to constraints.Integer that excludes ~uint8 and
> ~int8, it works fine. Explicit casting is no better, and there is no
> promotion (e.g., cast i to int and cast the result back to T) that's suitable
> for all integer types. I would like to shrink the block size for (u)int8, but
> there's no way to specialize the logic for specific types.
>
> I figured out that I can use i >> 9 instead of i / 512 in this instance,
> though there will be other cases (divide by non-Po2) where there isn't a
> simple workaround Is there a general way around this limitation?
It's not clear to me what is supposed to happen for the int8/uint8
case. It sounds like your block type won't work for int8/uint8. In
that case it seems like the right approach is to use a constraint that
doesn't permit it, as you suggest. What other kind of workaround
would be appropriate?
Ian
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