> On May 11, 2016, at 8:01 AM, Ricardo Parada via swift-evolution
> <[email protected]> wrote:
>> On May 10, 2016, at 2:53 PM, Chris Lattner <[email protected]
>> <mailto:[email protected]>> wrote:
>>
>> Hello Swift community,
>>
>> The review of "SE-0084: Allow trailing commas in parameter lists and tuples"
>> begins now and runs through May 16. The proposal is available here:
>>
>>
>> https://github.com/apple/swift-evolution/blob/master/proposals/0084-trailing-commas.md
>>
>> <https://github.com/apple/swift-evolution/blob/master/proposals/0084-trailing-commas.md>
>
>> * What is your evaluation of the proposal?
>
> -1
>
> I don’t like the proposal. I understand the flexibility it gives to
> rearranging elements but to someone reading the code it looks like an element
> was removed by mistake.
This objection is coming up quite often and I don't really see the difference
between trailing commas in collections (legal in Swift)
let listenerKeys: NSDictionary = [
AVFormatIDKey: NSNumber(unsignedInt: kAudioFormatAppleLossless),
AVSampleRateKey: 44100.0,
AVNumberOfChannelsKey: 1,
AVEncoderAudioQualityKey: NSNumber(int: Int32(AVAudioQuality.Max.rawValue)),
]
And trailing commas in parameter lists (not yet allowed in Swift):
public convenience init(
_ w: CGFloat,
_ h: CGFloat,
position: CGPoint = .zero,
backgroundColor: UIColor = UIColor.whiteColor(),
translucency alpha: CGFloat = 1.0,
borderWidth: CGFloat = 0.0,
borderColor: UIColor = UIColor.blackColor(),
cornerRadius: CGFloat = 0.0, // this is currently illegal
){
...
}
Neither example reads to me as if an element was removed by mistake. Both
greatly enhance programming flexibility. Both allow the final comma to be
omitted and/or the elements to be re-ordered.
To summarize the complaints to date:
* It make code read like errors
* Arrays and dictionaries are different "things" than parameters and tuples;
They are structurally different
* Parameter lists should always be of fixed size at deployment time; Once a
signature is fixed and consumed, it's difficult to change
To which I reply:
* Well structured code needn't read like an error. The examples above show an
in-house style that allows final commas. Your in-house style may differ and a
linter can catch these issues.
* Both collections and signatures are syntactically similar in layout even if
they are semantically different in use. In Swift, complex method signatures
with defaulted arguments like the example shown are not uncommon. Do not limit
your thinking to single line lists of (x: T, y: U, z: V) signatures.
* Parameter lists and function signatures, like collections, can evolve,
especially when using defaulted parameters, even when they are consumed at
multiple points.
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