Il giorno mar 27 mag 2025 alle ore 16:47 Thiago Macieira via Std-Proposals <
std-proposals_at_[hidden]> ha scritto:

> On Tuesday, 27 May 2025 10:32:13 Brasilia Standard Time Fabio Alemagna via
> Std-Proposals wrote:
> > Il giorno mar 27 mag 2025 alle ore 15:23 Thiago Macieira via
> Std-Proposals <
> > std-proposals_at_[hidden]> ha scritto:
> > > [...] An equality operator
> > > alone won't suffice, because then the order of case labels would
> matter,
> > > which
> > > seems ill-advised to me.
> >
> > Why would the order matter? You're looking for an item in a unordered
> set.
> > Of course, having other operators or even a hash function defined for the
> > specific type would make it possible to optimize the search.
>
> Because, with user types and weak ordering, two different entries in the
> case
> list could be equivalent to the sought item. That is, we could have A
> equiv. B
> and A equiv. C. Should the compiler require that therefore B equiv. C?
> Would
> it need to enforce that by performing the O(n²) checks at compile time, or
> would that just be declared UB or EB?
>

If the set is small, O(n²) might be acceptable, but performance would of
course improve by making the set ordered, or by implementing a hash
function for the type.

It's also plausible to me to make the order of case labels matter. It
really depends on the use case and the acceptable trade-off.

> As I've mentioned earlier, there's a library implementation of this. It
> can
> > of course be made better, but the core functionality is there. Have a
> look:
> > https://github.com/falemagn/uberswitch
>
> The fact that library implementations exist should indicate a core
> language
> construct isn't necessary.
>

That was actually my whole point. I'd explore the possibility to improve on
that library solution before attempting to extend the language with another
version of switch that overlaps with the pattern matching functionality.

Fabio