Open Radar

 
Summary:
I can use a trailing comma in a list of parameters to construct a Swift collect object like so:

        let foo = [
            "this",
            "that",
            "other",
        ]

I mean the comma after `"other"`. But I can't use a trailing comma in a function parameter list:

        let threeDoubles = String[](
            count: 3,
            repeatedValue: "",
        )

It's that comma after `""` that's not allowed. The error is "Expected expression in list of expressions". It would be nice to optionally be able to have that comma, especially if the arguments to a function are variadic: It's easier to add and remove arguments without having to remember to edit the final line. Diffs look better, too: only an added or removed line is highlighted; no need to highlight the addition or removal of a comma in the final line.

Most dynamic languages allow this syntax for lists of arguments, FWIW (though JavaScript and JSON notably don't, which is super irritating).

Steps to Reproduce:
1. Pass a list of arguments to a function
2. Put in a trailing comma


Expected Results:
No error.

Actual Results:
Compile-time error: Expected expression in list of expressions

Version:
Xcode 6

Notes:
Version 6.0 (6A215l)