If I'm not mistaken, the type of T can be inferred from the `next` closure
here. $0 is an optional, so you end up with a sequence of optionals.
> On 16 Aug 2016, at 00:51, Xiaodi Wu <xiaodi...@gmail.com> wrote:
>
> Given:
>
> let foo: T? = something()
> let bar = sequence(first: foo, next: { $0?.frobnicate() })
>
> If first could be of type `T` or `T?`, is bar of type `UnfoldSequence<T>` or
> `UnfoldSequence<T?>`?
>> On Mon, Aug 15, 2016 at 17:15 Tim Vermeulen via swift-evolution
>> <swift-evolution@swift.org> wrote:
>> I doubt that’s it, in no way is an an empty sequence inherently unsafe. The
>> entire standard library is built with empty sequences in mind. I’m more
>> inclined to think it’s an oversight.
>>
>>> On 15 Aug 2016, at 23:15, Maximilian Hünenberger <m.huenenber...@me.com>
>>> wrote:
>>>
>>> Ok, I see. However this could be a potential source of bugs/performance
>>> issues where you don't consider the nil case and you do some unnecessary
>>> work. By prohibiting to pass nil you have to manually unwrap and you
>>> immediately see the "optionality".
>>>
>>>> Am 15.08.2016 um 22:36 schrieb Tim Vermeulen <tvermeu...@me.com>:
>>>>
>>>> Oh, that’s true, I misunderstood your previous message. It’s not about
>>>> passing nil, but it’s about passing optionals. The point is to be able to
>>>> do something like this:
>>>>
>>>> let number = functionThatReturnsAnOptional()
>>>> sequence(first: number, next: { $0 % 2 == 0 ? $0 / 2 : nil })
>>>>
>>>>> On 15 Aug 2016, at 22:26, Maximilian Hünenberger <m.huenenber...@me.com>
>>>>> wrote:
>>>>>
>>>>> Probably I didn't understand your proposal. What do you want to change
>>>>> exactly?
>>>>>
>>>>> I thought:
>>>>> public func sequence<T>(first: T, next: @escaping (T) -> T?) ->
>>>>> UnfoldFirstSequence<T> { ... }
>>>>>
>>>>> To:
>>>>> public func sequence<T>(first: T?, next: @escaping (T) -> T?) ->
>>>>> UnfoldFirstSequence<T> { ... }
>>>>>
>>>>>> Am 15.08.2016 um 22:17 schrieb Tim Vermeulen <tvermeu...@me.com>:
>>>>>>
>>>>>> You can’t; the `first` parameter has type `T`, not `T?`.
>>>>>>
>>>>>>> On 15 Aug 2016, at 22:10, Maximilian Hünenberger
>>>>>>> <m.huenenber...@me.com> wrote:
>>>>>>>
>>>>>>> Hi Tim,
>>>>>>>
>>>>>>> If you pass "nil" to "first" isn't this an empty sequence? So it would
>>>>>>> be redundant.
>>>>>>>
>>>>>>> Best regards
>>>>>>> Maximilian
>>>>>>>
>>>>>>>> Am 15.08.2016 um 01:27 schrieb Tim Vermeulen via swift-evolution
>>>>>>>> <swift-evolution@swift.org>:
>>>>>>>>
>>>>>>>> sequence(first:next:) takes a non-optional first argument. Is there a
>>>>>>>> reason for that? sequence(state:next:) allows empty sequences, and I
>>>>>>>> don’t see why sequence(first:next:) shouldn’t. The fix would be to
>>>>>>>> simply add the `?` in the function signature; no other changes are
>>>>>>>> required to make it work.
>>>>>>>>
>>>>>>>> I considered just filing a bug report, but since this is a change of
>>>>>>>> the public API...
>>>>>>>> _______________________________________________
>>>>>>>> swift-evolution mailing list
>>>>>>>> swift-evolution@swift.org
>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>
>>>>
>>
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution@swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
_______________________________________________
swift-evolution mailing list
swift-evolution@swift.org
https://lists.swift.org/mailman/listinfo/swift-evolution
