[swift-evolution] ternary operator ?: suggestion

[Paul Ossenbruggen]

Been thinking about the boolean case a bit more, and how to make it better than a ternary using my proposed syntax. So else could be put there to help show it is the opposite. The downside is this makes it mix keywords and operators so seems a bit jarring. 

With the new form parenthesis are built into it and are required:

x = ?(x == y : 49 else 3) 
alternatively the bang means do the opposite:

x = ?(x == y : 49 ! 3) // not sure this creates a parsing problem. 
or if the above causes a parsing problem:

x = ?(x == y : 49 | 3)  
Any thoughts?

> On Dec 23, 2015, at 7:02 AM, Félix Cloutier via swift-evolution <swift-evolution at swift.org> wrote:
> 
> I know, but that won't support pattern matching.
> 
> Félix
> 
>> Le 23 déc. 2015 à 02:22:07, David Waite <david at alkaline-solutions.com <mailto:david at alkaline-solutions.com>> a écrit :
>> 
>> In the case where your input is hashable, you could just do:
>> 
>> let i = [.Red:0xff0000, .Green:0x00ff00, .Blue:0x0000ff][color]
>> 
>> this would mean that color must be a Color and not an Optional<Color> (because of swift 2.x limitations)
>> 
>> -DW
>> 
>>> On Dec 22, 2015, at 8:04 AM, Félix Cloutier via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>> 
>>> I like the gist of it too, though you seem to introduce both a new keyword and a new syntax. (To be clear, I like the syntax but I'm ambivalent towards reusing switch instead of which.)
>>> 
>>> My minor suggestions would to avoid braces for things that aren't scopes; that either the comma or the the question mark is redundant in their current position (you need a start delimiter or an end delimiter but you don't need both); and that it needs a way to handle a default case if enumeration isn't exhaustive (I'd do that by returning an optional).
>>> 
>>>> let i = which color (.Red: 0xff0000, .Green: 0x00ff00, .Blue: 0x0000ff) ?? 0x000000
>>> 
>>> 
>>> Thinking out loud, once you remove the question marks it really looks like a dictionary literal, so maybe it could even use square brackets to close the gap.
>>> 
>>>> let i = which color [.Red: 0xff0000, .Green: 0x00ff00, .Blue: 0x0000ff] ?? 0x000000
>>> 
>>> 
>>> I thought about subscripting a dictionary literal in place:
>>> 
>>>> [Color.Red: 0xff0000, ...][color] ?? 0x000000
>>> 
>>> 
>>> but that won't support elaborate pattern matching, and I think that this is a deal breaker for the functional folks.
>>> 
>>> Félix
>>> 
>>>> Le 22 déc. 2015 à 09:31:32, Charles Constant <charles at charlesism.com <mailto:charles at charlesism.com>> a écrit :
>>>> 
>>>> Just goofing on this a little. What if we called it a "which" statement, instead of a "switch" statement? It's a bit cutesy, but not too verbose, and it makes sense if you read it aloud.
>>>> 
>>>> let i = which color {
>>>> 	? .Red: 0xFF0000, 
>>>> 	? .Green: 0x00FF00, 
>>>> 	? .Blue: 0x00000FF
>>>> }
>>>> 
>>>> let i = which boo {
>>>> 	? true: 1, 
>>>> 	? false: 0, 
>>>> 	? nil: -1
>>>> }
>>>> 
>>> 
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> 
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