[swift-evolution] Switch statement tuple labels

[Derrick Ho]

In your first example the switch statement is evaluating whether the given
tuple of type (_:bool, _:bool) matches another tuple of type (_: bool, y:
bool)

The type signature doesn't match.

I believe the change would not be additive like you say because it seems
like it would require a change in how tuple compare with each other.


On Mon, Jan 2, 2017 at 12:00 AM Erica Sadun via swift-evolution <
swift-evolution at swift.org> wrote:

> Well, it turns out, I was testing it on already established values. The
> first of the following two examples works but the second does not.
>
> switch (true, y: false) {
> case (true, y: false): print("tf")
> default: print("nope")
> }
>
> let testTuple2 = (true, false)
>
> switch testTuple2 {
> // error: tuple pattern element label 'y' must be '_'
> case (true, y: false): print("tf")
> default: print("nope")
> }
>
> I think this gets a 95% Emily Litella (
> https://en.wikipedia.org/wiki/Emily_Litella). "Nevermind."
>
> And thanks, Tony,
>
> -- E
>
>
> On Jan 1, 2017, at 8:49 PM, Tony Allevato <tony.allevato at gmail.com> wrote:
>
> The "after" example you posted seems to work already in Swift today. Is
> there something I'm missing?
>
>
> On Sun, Jan 1, 2017 at 7:35 PM David Sweeris via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
>
> Sent from my iPhone
>
> On Jan 1, 2017, at 19:25, Erica Sadun via swift-evolution <
> swift-evolution at swift.org> wrote:
>
> Was helping a friend with some code and got inspired. I decided to throw
> this on list to see if there's any traction.
>
> *Idea*: Introduce optional argument labels to tuples in switch statements
>
> *Motivation*: Cases can be less readable when pattern matching tuples.
> Semantically sugared, optional argument labels could increase readability
> for complex `switch` statements by incorporating roles into cases.
>
> Here's an example before:
>
> fileprivate func chargeState(for battery: BatteryService)
>     -> ChargeState
> {
>     switch (battery.state, battery.isCalculating) {
>     case (.isACPowered, true):
>         return .calculating(isDischarging: false)
>     case (.isACPowered, _) where battery.isCharging:
>         return .charging
>     case (.isACPowered, _):
>         return .acPower
>     case (_, true):
>         return .calculating(isDischarging: true)
>     default:
>         return .batteryPower
>     }
> }
>
>
> and after:
>
> fileprivate func chargeState(for battery: BatteryService)
>     -> ChargeState
> {
>     switch (battery.state, *calculating: battery.isCalculating*) {
>     case (.isACPowered, *calculating: true*):
>         return .calculating(isDischarging: false)
>     case (.isACPowered, _) where battery.isCharging:
>         return .charging
>     case (.isACPowered, _):
>         return .acPower
>     case (_, *calculating: true*):
>         return .calculating(isDischarging: true)
>     default:
>         return .batteryPower
>     }
> }
>
>
> It's a pretty minor change, and I could see it being added to allow case
> statements to be more readable with a minimal change to the compiler. I
> also have a back-burnered proposal I intend to introduce in Phase 2 that
> would introduce Boolean raw value enumerations for flags.
>
> Thoughts?
>
>
> I can't think of a reason not to do that... +1
>
> - Dave Sweeris
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