SE-0284: Allow Multiple Variadic Parameters in Functions, Subscripts, and Initializers

Evolution Proposal Reviews
8 
// Before
try assertArgs("swift", "-foo", "-bar", parseTo: .interactive, leaving: ["-foo", "-bar"])
// After
try assertArgs("swift", "-foo", "-bar", parseTo: .interactive, leaving: "-foo", "-bar")

This results in a cleaner, more consistent interface.

I'm puzzled by the example and the conclusion here. IMO the Before case is a clear win in terms of understanding when I'm looking at the call-site. The After case makes it look like "-bar" is a separate unlabeled argument. The [ ] delimiters in the Before case make it clear that "-bar" is part of the argument labeled leaving:.

If I were a project maintainer, I would flag this during code review as a negative. If eliding a couple of brackets leads to ambiguity when reading, might as well write those two brackets. One can use array arguments in both places if one strongly desires consistency.

myView.addSubviews(v1, v2, constraints: v1.widthAnchor.constraint(equalTo: v2.widthAnchor),
                                        v1.heightAnchor.constraint(equalToConstant: 40),
                                        /* More Constraints... */)

This example seems hand-formatted... how is a code formatter supposed to format it this way? With long lines, what is most likely going to happen is something like:

myView.addSubviews(
    v1,
    v2,
    constraints: myVeryVeryVeryVeryLooooooooooooooooongConstraint,
    myOtherVeryVeryLooooooooooongConstraintExpression
)

:slightly_frowning_face: Again the same problem comes up. While reading, someone is likely to misunderstand what is going on. Making the formatting like the hand-formatted example requires a code formatter to do non-trivial semantic analysis. Does swift-format already do this?

Having an array sidesteps the issue:

myView.addSubviews(
    v1,
    v2,
    constraints: [
        myVeryVeryVeryVeryLooooooooooooooooongConstraint,
        myOtherVeryVeryLooooooooooongConstraintExpression
    ]
)

When I started reading the proposal, I was ambivalent about it but looking at the examples makes me think it is a bad idea.

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