[swift-evolution] [Review] SE-0084: Allow trailing commas in parameter lists and tuples

[L. Mihalkovic]

> On May 13, 2016, at 8:31 AM, Patrick Smith via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I forgot to add I like this style particularly as it matches how the type is declared (below). There’s a symmetry between them all. Obviously each var in a struct doesn’t need a comma between it, so it would be nice to not have to type them in the other cases too!
> 
> public struct ImageGraphic : GraphicType {
>    var imageSource: ImageSource
>    var width: Dimension?
>    var height: Dimension?
> }
> 

Hate to admit it (i write my code such that i can use ", xxxx" as a search pattern, especially with editors/IDEs that have a poot level of understanding of what I am typing - Did I mention somewhere this idea of a new @string_literal("text/json") attribute to help them make some sense of what those magic quoted-holes contain??!), but I actually am growing fonder of this by the day... I can even find it logical considering other grammar-fragments use the same heuristic to get rid of their own separation markers (like ;)


> 
>> On 13 May 2016, at 4:22 PM, Vladimir.S <svabox at gmail.com> wrote:
>> 
>> It seems like all problems could be solved by allowing line-break instead of comma in list:
>> 
>>    public init(source: JSONObjectDecoder) throws {
>>        try self.init(
>>            imageSource: source.decode("imageSource")
>>            width: source.decodeOptional("width")
>>            height: source.decodeOptional("height")
>>        )
>>    }
>>    
>>    public func toJSON() -> JSON {
>>        return .ObjectValue([
>>            "imageSource": imageSource.toJSON()
>>            "width": width.toJSON()
>>            "height": height.toJSON()
>>        ])
>>    }
>> 
>> Shouldn't we move in that direction? Probably in addition to allow trailing comma just to allow one to use his/her preferable formatting
>> 
>>> On 13.05.2016 9:07, Patrick Smith via swift-evolution wrote:
>>> I do it quite a lot, especially for initialising structs, enums. I use it to get the same benefits as a switch statement spread over several lines.
>>> 
>>> I think it’s often good to liberally apply new lines, as it aids legibility.
>>> 
>>> Here some sample code of mine using it:
>>> 
>>> extension ImageGraphic : JSONObjectRepresentable {
>>>    public init(source: JSONObjectDecoder) throws {
>>>        try self.init(
>>>            imageSource: source.decode("imageSource"),
>>>            width: source.decodeOptional("width"),
>>>            height: source.decodeOptional("height")
>>>        )
>>>    }
>>>    
>>>    public func toJSON() -> JSON {
>>>        return .ObjectValue([
>>>            "imageSource": imageSource.toJSON(),
>>>            "width": width.toJSON(),
>>>            "height": height.toJSON()
>>>        ])
>>>    }
>>> }
>>> 
>>> 
>>>> On 13 May 2016, at 3:01 PM, Chris Lattner via swift-evolution <swift-evolution at swift.org> wrote:
>>>> 
>>>> On May 12, 2016, at 4:50 PM, Joe Groff <jgroff at apple.com> wrote:
>>>>>>>    --- a.swift
>>>>>>>    +++ a.swift
>>>>>>>     foo(
>>>>>>>       x: 0,
>>>>>>>    -  y: 1
>>>>>>>    +  y: 1,
>>>>>>>    +  z: 2
>>>>>>>     )
>>>>>>> 
>>>>>>> Trailing commas avoid this:
>>>>>>> 
>>>>>>>    --- a.swift
>>>>>>>    +++ a.swift
>>>>>>>     foo(
>>>>>>>       x: 0,
>>>>>>>       y: 1,
>>>>>>>    +  z: 2,
>>>>>>>     )
>>>>>> 
>>>>>> You’re arguing that you want to read Swift code written like this?
>>>>> 
>>>>> I wouldn't mind it.
>>>> 
>>>> I personally find that style repulsive :-) and I haven’t seen swift code commonly doing it.  I’m not sure that we want to encourage it either.
>>>> 
>>>>> The standard library already uses this style for function parameters, modulo the trailing comma, and I certainly prefer it to:
>>>>>    
>>>>>>    --- a.swift
>>>>>>    +++ a.swift
>>>>>>     foo( x: 0
>>>>>>        , y: 1
>>>>>>    +   , z: 2
>>>>>>        )
>>>> 
>>>> I agree that this is even worse, but I also haven’t seen this used in Swift code.  Have you?   Swift’s strictness with argument labels makes any of this pretty unappealing to use.
>>>> 
>>>> If we were really concerned about this, a narrower way to solve the same problem would be to allow a comma before the ), but *only* when there is a newline between them.  I still don’t see why we’d want to encourage this though.
>>>> 
>>>> -Chris
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>>> 
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