On Mon, 15 Jun 2026 at 12:28, Levi Morrison <[email protected]> wrote:
> > Voting is now open on the Bound-Erased Generic Types RFC, as announced > > in the Intent to Vote message earlier this week. > > > > The vote started on 2026-06-14 at 16:50 UTC and ends on 2026-06-28 at > 17:00 UTC. > > > > RFC: https://wiki.php.net/rfc/bound_erased_generic_types > > Discussion thread: https://news-web.php.net/php.internals/130816 > > Implementation: https://github.com/php/php-src/pull/21969 > > To my own surprise, I am voting yes on this proposal. > > I still believe that refied generics should be the goal. To that end, > I think we should be able to merge this and in minor versions, fix > "soundness" and implementation holes as "bug" fixes on that route. If > internals can agree on this, and then the community can communicate > this through education, promotion, documentation, etc, then this RFC > is simply a useful stepping stone. > > This is based on my own experience playing with the RFC, which > included reporting 2 bugs in the implementation on the RFC. To be > honest, it's not too useful to me. I very quickly run up against some > limitation when trying to build useful things. Most notably, we need > to be able to define lower bounds (syntax pending, obviously): > > class Option<+A> > { > // B >: A means B is an ancestor of A > // Since all As are Bs, you can return the A here > function get_or_default<B >: A>(Option $option, B $default): B > { > return $option->has_some() > ? $option->get() > : $default; > } > // todo: the rest of the implementation > } > > You can't take `A $default` and return `A` because this violates the > variance laws: a covariant type A cannot be used in parameter > position. So alternatively you could solve this with `inout A > $default` or similar. > Presumably this would work with the current proposal: class Option<+A> { public function getOrDefault<B>(B $default): A|B { return $this->hasSome() ? $this->get() : $default; } } Hack also has `super` type constraints: https://hhvm.com/blog/9215/covariance-contravariance-and-super-type-constraints
