> On Jun 1, 2016, at 6:26 AM, Matthew Johnson <[email protected]> wrote: > >> >> On Jun 1, 2016, at 8:18 AM, Joe Groff via swift-evolution >> <[email protected]> wrote: >> >>> >>> On May 31, 2016, at 6:49 PM, Austin Zheng <[email protected]> wrote: >>> >>> I agree that this is a better design for Swift than the monstrosity I >>> started out with. >>> >>> The "biggest" technical challenge I see is being able to type a reduction >>> sort of operator on a heterogenous tuple based on on whatever protocols and >>> constraints are common to its constituent members. For example: >>> >>> // Every Tn in T... is Fooable and Barrable >>> let x : (T...) >>> reduce(x, reducer, startingValue) >>> >>> func reducer<X : ???>(startingValue: U, eachMemberOfT: X) -> U { ... } >>> >>> How do we bound ??? such that 'reducer' is useful while still being >>> statically type sound? Honestly, that's the most interesting question to >>> me. Generalized existentials might help with that. >> >> If every T is Fooable and Barrable, couldn't `eachMemberOfT` be (inout U, >> protocol<Fooable, Barrable>) -> ()? >> >>> Other questions (inherent to any proposal) would be: >>> >>> - How do we resolve the impedance mismatch between tuples and function >>> argument lists? Is it even worth trying to resolve this mismatch, given >>> that argument lists are intentionally not intended to mirror tuples? >> >> The impedance mismatch between function arguments and tuples is superficial. >> You ought to be able to splat and bind tuples into function arguments, e.g.: >> >> let args = (1, 2) >> foo(bar:bas:)(args...) >> >> func variadicFn<T: Runcible...>(_ args: T...) { … } > > Going this direction is relatively straightforward. The impedance mismatch > is trickier when you want to do more than that. For example, it would be > extremely useful to come up with some way to wrap a function that has > parameters with default arguments without requiring callers of the wrapped > function to supply arguments for the defaulted parameters. Any ideas on how > to solve that?
As Chris noted, that sounds like a great use case for a macro. Trying to do that with the type system feels like it's on the wrong side of the complexity threshold to me. -Joe >> >>> - As you said, how do variadic generics work in the 0- and 1-member cases? >> >> What problem are you referring to? >> >> -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
