Do you mean you want a default closure?
func forEach<U,T>(transform: (U)->T = { return $0 }, do: (T)->Void)
doSomething {
if let g = $0 as? Giraffe { g.eatTheTallLeaves() }
}
doSomething(transform: { $0 as! Giraffe }) {
$0.eatTheTallLeaves()
}
> On 6 Jan 2017, at 15:28, Jay Abbott via swift-evolution
> <[email protected]> wrote:
>
> Some good arguments regarding warnings and multiple closures. But I can't
> help that feel when designing an API, if you have to add a convenience method
> that takes just one closure simply to call the real method, this is exactly
> the sort of boilerplate code that default arguments are supposed to replace.
>
> On Thu, 5 Jan 2017 at 05:48 Douglas Gregor <[email protected]
> <mailto:[email protected]>> wrote:
>> On Jan 4, 2017, at 9:44 PM, Saagar Jha <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> So, then this should have a warning? I’m still not getting one.
>>
>> func foo(a: () -> (), b: (() -> ())? = nil, c: Int) {
>> a()
>> b?()
>> }
>>
>> foo(a: {
>> print(“Bar”)
>> }, c: 0)
>>
>
> If you give “c” a default value (e.g., “= 0”), it will give a warning.
>
> I’m happy for the warning to get more eager, so long as it also gets a Fix-It
> at the same time.
>
> - Doug
>
>> Saagar Jha
>>
>>
>>
>>> On Jan 4, 2017, at 9:34 PM, Douglas Gregor <[email protected]
>>> <mailto:[email protected]>> wrote:
>>>
>>>
>>>> On Jan 4, 2017, at 9:32 PM, Saagar Jha <[email protected]
>>>> <mailto:[email protected]>> wrote:
>>>>
>>>>
>>>>
>>>> Saagar Jha
>>>>
>>>>
>>>>
>>>>> On Jan 4, 2017, at 8:35 PM, Douglas Gregor <[email protected]
>>>>> <mailto:[email protected]>> wrote:
>>>>>
>>>>>
>>>>> On Jan 4, 2017, at 7:48 PM, Saagar Jha via swift-evolution
>>>>> <[email protected] <mailto:[email protected]>> wrote:
>>>>>
>>>>>> Check out this thread
>>>>>> <https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160606/020470.html>–it’s
>>>>>> very similar to what you proposed, but it didn’t go anywhere. FWIW +1
>>>>>> to this as well as the ability to use multiple trailing closures like so:
>>>>>>
>>>>>> animate(identifier: “”, duration: 0, update: {
>>>>>> // update
>>>>>> }, completion: {
>>>>>> // completion
>>>>>> }
>>>>>>
>>>>>> Saagar Jha
>>>>>>
>>>>>>
>>>>>>
>>>>>>> On Jan 4, 2017, at 6:25 PM, Jay Abbott via swift-evolution
>>>>>>> <[email protected] <mailto:[email protected]>> wrote:
>>>>>>>
>>>>>>> When you have a function with a closure and then another optional
>>>>>>> default = nil closure at the end, like this:
>>>>>>>
>>>>>>> open static func animate(identifier: String,
>>>>>>> duration: Double,
>>>>>>> update: @escaping AnimationUpdate,
>>>>>>> completion: AnimationCompletion? = nil) {
>>>>>>> You can’t use trailing closure syntax for the update argument when
>>>>>>> leaving the completion argument out/default.
>>>>>>>
>>>>>>> This kind of breaks one of the benefits of default arguments, which is
>>>>>>> that you can add them to existing released functions without breaking
>>>>>>> the calling code. This means you have to add a separate convenience
>>>>>>> function without the extra argument, which is annoying and inelegant.
>>>>>>>
>>>>> Why not simply add the "completion" parameter before the trailing
>>>>> closure? That would still allow existing callers to work, without having
>>>>> to change the language.
>>>>>
>>>>>>> Another annoying thing is that you can easily miss this error if you
>>>>>>> happen to not use trailing closure syntax in your tests or other usage,
>>>>>>> because adding the extra default argument compiles fine for code that
>>>>>>> uses normal syntax.
>>>>>>>
>>>>> The Swift compiler warns when a parameter written as a closure type isn't
>>>>> the last parameter. The warning is actually disabled in the specific case
>>>>> above because you've written it using a typealias... maybe we should warn
>>>>> on such cases (it's worth a bug report). Regardless, in the majority of
>>>>> instances, you'll get a warning, so it won't be silent on disabling
>>>>> trailing closure syntax.
>>>>
>>>> Tried this out in the playground:
>>>>
>>>> func foo(a: () -> (), b: (() -> ())? = nil) {
>>>> a()
>>>> b?()
>>>> }
>>>>
>>>> foo(a: {
>>>> print(“Bar”)
>>>> })
>>>>
>>>> and didn’t receive a warning for it, either.
>>>
>>> We don’t warn here because ‘foo’ does have a trailing closure… it’s for the
>>> second parameter. I guess we could still warn about ‘a’ (maybe lump it into
>>> the same bug about the typealias case).
>>>
>>> - Doug
>>>
>>
>
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