[swift-evolution] Switch statement tuple labels

[Erica Sadun]

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 <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 <mailto: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 <mailto: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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