I think the rationale thread for the original version of this proposal pretty much shut down the possibility of disjunctive type constraints. In fact, the primary argument against '&' was that it would encourage conversations about '|'.
It's also been added to the commonly rejected proposals list: https://github.com/apple/swift-evolution/blob/master/commonly_proposed.md On Mon, Jun 27, 2016 at 9:48 AM, Joe Groff via swift-evolution < [email protected]> wrote: > > > On Jun 25, 2016, at 12:00 AM, L. Mihalkovic < > [email protected]> wrote: > > > > Inline > > Regards > > (From mobile) > > > >> On Jun 25, 2016, at 1:00 AM, Joe Groff via swift-evolution < > [email protected]> wrote: > >> > >> > >>> On Jun 23, 2016, at 8:55 PM, Jordan Rose via swift-evolution < > [email protected]> wrote: > >>> > >>> [Proposal: > https://github.com/apple/swift-evolution/blob/master/proposals/0095-any-as-existential.md > ] > >>> > >>> I’ve gone on record before as against this syntax, although when I set > out earlier today to record my usual rebuttal I found that it really was > mostly a matter of taste. Yes, this looks weird to me: > >>> > >>> let callback: (Data) -> NSCoding & NSCopying > >>> > >>> but I’m sure the infix ‘->’ for functions looked weird to everyone the > first time they saw it as well, and it really is pretty clear in argument > position. > >> > >> We could conceivably bracket the 'where' constraints somewhere. It's > nice not to have to punish the common case syntax. In my personal ideal > vision of the world, I'd like to see us support opening existentials via > path-dependent types (e.g., let a: Collection; let element: a.Element). If > we support them in decl-level 'where' clauses, we provide a nice, clean > syntax for complex generic relationships that doesn't require angle > brackets or per-existential where clauses at all, something like: > >> > >> func intersect(a: Collection, b: Collection) -> Collection > >> where a.Element == b.Element, b.Element == return.Element { > >> } > >> > >> which doesn't completely define away the need for 'where' as part of > existential types, but would shrink it quite a bit. > > > > For some reason it had not clicked until your 'path dependent type' > reference how reminicent of (U+00B7) this is. I watched nada's 2014 > presentation again... but then it means intersection types would add a > lot... you guys seem ok to add P&Q now, so why not take that opportunity to > allow P|Q at the same time. Does it also mean that you might consider at > some point expanding 'assoctype U' into: T where <:U , :>U opening the > door to lower/higher type bounds? > > Let's not rathole on the P|Q thing. Disjunctions are difficult to make > much sense of in a parametric type system like ours; there are plenty of > other threads on this mailing list discussing it. > > -Joe > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution >
_______________________________________________ swift-evolution mailing list [email protected] https://lists.swift.org/mailman/listinfo/swift-evolution
