> On Jun 6, 2017, at 1:59 PM, Stephen Celis <[email protected]> wrote:
>
>> On Jun 6, 2017, at 1:43 PM, Mark Lacey via swift-evolution
>> <[email protected]> wrote:
>>
>> Unless I am missing something this is an example of tuple destructuring. I’m
>> looking for examples of other issues.
>
> The destructuring issue is the most pervasive, but as mentioned it also
> breaks point-free style:
>
> https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20170529/036911.html
>
> Again, less common for most but heavily used by us and folks that use
> functional patterns and libs like RxSwift, ReactiveCocoa, etc., where a lot
> of streams/signals of values are composed into new structures.
Thanks for reminding me. It’s good to call out this case specifically. The
underlying reason that this is disallowed for Swift 4 is the same as the
underlying reason that a closure immediately passed as an argument (with with
mismatching function type) is disallowed for Swift 4 (i.e. the “tuple
destructuring” case). It might be possible to relax restrictions to allow one
of these without allowing the other.
Having said that, I find it surprising that your tupleUp function works as it
is implicitly converting the function type in a way that I would expect SE-0110
to disallow. My expectation is that it would need to be written like this:
func tupleUp<A, B, C>(_ f: @escaping (A, B) -> C) -> ((A, B)) -> C {
return { f($0.0, $0.1) }
}
Mark
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