[swift-evolution] [Pitch] Use "where" in combination with "??" to provide Ternary-like functionality

[charles@charlesism.com]

I'm not actually familiar with the term "tri op" but if you're referring to the ternary, it's only useful when you two, or three items. 

If you chain a ternary to use more than three options it becomes error-prone and almost impossible for a human to read

When I'm at my desktop I'll add a couple better examples of what I'm proposing. 

Sent from my iPhone

> On May 23, 2016, at 6:18 PM, Dany St-Amant <dsa.mls at icloud.com> wrote:
> 
> 
> Why reinvent the wheel, when the old trusty (but a bit cryptic according to some) tri-op can do the trick…
> 
>> Le 23 mai 2016 à 04:29, Charles Constant via swift-evolution <swift-evolution at swift.org> a écrit :
>> 
>> Here's a few examples of what this change would allow. 
>> 
>> I just plucked the first instances of other people's switch statements that I found on GitHub. 
>> 
>> If there were an easy way to search GitHub for chained ternary expressions, I would have added some examples of those too, since they could all be improved with this where clause + ??. 
>> 
>> 
>> 	mutating func toggle() {
>> 		switch self{
>> 		case Off:
>> 			self = On
>> 		case On:
>> 			self = Off	
>> 		}	
>> 	}
>> 
>> 
>> 
>> 	mutating func toggle() {
>> 		self = .On where (self == .Off) ?? .Off
>> 	}
> 
> mutating func toggle() { self = self == .Off ? .On : .Off }
> 
>> 
>> 	switch switchNumberThree {
>> 		case 10, 11, 12:
>> 			println("It is \(switchNumberThree)")
>> 		default:
>> 			("It is none of them!")
>> 	}
>> 
>> 
>> 	println(
>> 		"It is \(switchNumberThree)" where 10...12 ~= switchNumberThree
>> 		?? "It is none of them!"
>> 	)
> 
> print( 10...12 ~= switchNumberThree ? "It is \(switchNumberThree)"
>        : "It's none of them" )
> 
>> 
>> 	switch x {
>> 	case 1:
>> 		j++
>> 	case 2:
>> 		j++
>> 	case 3:
>> 		j++
>> 	case 4:
>> 		j++
>> 		fallthrough
>> 	case 5:
>> 		j++
>> 		fallthrough
>> 	default:
>> 		j++
>> 	}
>> 
>> 
>> 	j = j+1 where (4...5 ~= x) ?? j+2
> 
> Broken conversion:
> j += 4...5 ~= x ? 1 : 2
> 
> Proper conversion:
> j += 4 ~= x ? 3 : 5 ~= x ? 2 : 1
> 
> Earlier e-mail example:
>>     let foo = 
>>         "positive" where ( bar > 0 )  ?? 
>>         "negative" where ( bar < 0 ) ?? 
>>         "zero"
> 
> let foo = bar > 0 ? "positive" :
>           bar < 0 ? "negative" :
>           "zero"
> 
> Dany
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