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

[Patrick Smith]

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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