> On Sep 5, 2017, at 18:14, Slava Pestov <spes...@apple.com> wrote: > > >> On Sep 5, 2017, at 1:01 PM, David Zarzycki via swift-dev >> <swift-dev@swift.org> wrote: >> >> Hi Jordan, >> >> Thanks for thinking about this. For whatever it may be worth, I’m concerned >> about 1) the ability to reorder declarations and 2) the “either/or” nature >> of this proposal. >> >> First, reordering: The ability to reorder declarations is deeply ingrained >> into the subconsciousness of Swift programmers and for good reasons. > > There are a couple of other places where ordering of declarations matters in > the ABI. The two most important ones I can think of right now are virtual > methods and protocol methods. Both are called by performing an indexed lookup > into a vtable. For methods, we were thinking that the ordering should first > sort by availability annotation, and then by the mangled name of the method. > This would allow re-ordering as well as adding new methods, as long as they > had a ‘newer’ availability than anything that has come before. > > However, I like the idea of an @_abi (or similar) attribute as an escape > hatch of some kind, in case we screw something up.
Ya, given how vtables work, the ABI is essentially API once ABI-stability matters. Having something like "@_slot() func” and "@_slots() class” would also yield a nice “belt and suspenders” approach for those people that want to enable ABI stability on a given declaration. If anything, given how many methods exist on classes and the strong desire to reorder methods, the “@_slot()” attribute would be really nice. Dave _______________________________________________ swift-dev mailing list swift-dev@swift.org https://lists.swift.org/mailman/listinfo/swift-dev
