On Thu, Aug 06, 2020 at 01:07:14PM +0000, Per Nordlöw via Digitalmars-d-learn
wrote:
[...]
> However, your solution
>
> template maxSize(T...)
> {
> align(1) union Impl { T t; }
> enum maxSize = Impl.sizeof;
> }
>
> fails as
>
> variable `std.variant.maxSize!(void, string).Impl.__t_field_0`
> variables cannot be of type `void`
>
> because one of the instances of `maxSize` in std.variant has `void` as
> a member `T...`.
Ugh, apparently `void` is one of those nasty inconsistent things that
has all sorts of ad hoc behaviour:
- void cannot be used to instantiate variables (behaves sortof like a
bottom type);
- But in spite of that, void.sizeof == 1, rather than the expected 0. My
guess is that this has to do with the hack to make the size of void[]
equal to its length;
- void in void[] is a top type (but only in that context -- but its
.sizeof is inconsistent with this);
- void is a unit type when specified as a function return type (but in
spite of that cannot be instantiated, contrary to a true unit type,
and this contradicts its being a top type in void[]);
IOW, void is a mishmash of ad hoc things thrown together in a way that
isn't even self-consistent. A chimera of exceptions that, it would seem,
always require special-casing to handle.
> Do you have any simple solution to this, H. S. Teoh?
Unfortunately, no. :-( Why does std.variant even support storing void
in the first place?!
T
--
People tell me that I'm paranoid, but they're just out to get me.
