> On May 27, 2016, at 5:19 PM, Brent Royal-Gordon via swift-evolution
> <swift-evolution@swift.org> wrote:
>
>>> - A plain `with` whose closure parameter is not mutable and which is marked
>>> `@discardableResult`.
>>
>> I would like to see this version restricted to AnyObject. It has extremely
>> limited utility with value types. It would usually be a mistake to call it
>> with a value type.
>
> I would not. It gives you a way to give a value type a short, scoped,
> immutable alias:
>
> with(RareMagicalDeviceOwner.shared.spimsterWickets[randomIndex]) {
> print($0.turns)
> print($0.turnSpeed)
> }
>
> And in this form, there is no danger of mistakenly mutating the value type,
> because mutating methods would not be allowed:
>
> with(RareMagicalDeviceOwner.shared.spimsterWickets[randomIndex]) {
> $0.turnRepeatedly(times: 3) // Error: can't call mutating
> method on immutable parameter
> }
>
> To be clear, I'm not convinced there's a need to make any change from the
> proposed version at all. I'm spitballing alternate designs here, trying to
> see if there might be something a little better out there. But so far, I
> think the proposal balances the feature size against strictness pretty well,
> whereas these stricter designs I'm discussing increase the surface of the
> feature more than they improve it. This is a small (but significant!)
> convenience, and I feel pretty strongly that it should have a small
> implementation.
>
>> That said, I am not convinced these non-copying functions would be worth
>> having after method cascades are introduced. Are there any use cases left
>> for them in that future?
>
> Yes, absolutely. Method cascades have a narrow use case: methods on `self`.
> Not everything in Swift is a method, and not all methods are on `self`.
>
> with(tableView.cellForRow(at: indexPath).myLabel) { label in
> print("Constraining label: \(label)")
>
> NSLayoutConstraint.activate(
> NSLayoutConstraint.withVisualFormat("|-[label]-|",
> options: [], metrics: [:], views: ["label": label]) +
> NSLayoutConstraint.withVisualFormat("V:|[label]|",
> options: [], metrics: [:], views: ["label": label])
> )
>
> constrainedLabels.append(label)
> }
>
> None of the calls in that `with` block would benefit from method cascades,
> but they all benefit from `with`.
What are the differences or benefits of the above examples over the existing
`do { let ... }` form?
do {
let w = RareMagicalDeviceOwner.shared.spimsterWickets[randomIndex]
print(w.turns)
print(w.turnSpeed)
}
do {
let label = tableView.cellForRow(at: indexPath).myLabel
print("Constraining label: \(label)")
NSLayoutConstraint.activate(
NSLayoutConstraint.withVisualFormat("|-[label]-|", options: [],
metrics: [:], views: ["label": label]) +
NSLayoutConstraint.withVisualFormat("V:|[label]|", options: [],
metrics: [:], views: ["label": label])
)
constrainedLabels.append(label)
}
--
Greg Parker gpar...@apple.com Runtime Wrangler
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