[swift-evolution] ternary operator ?: suggestion

[Paul Ossenbruggen]

> On Dec 13, 2015, at 6:11 AM, Marc Knaup <marc at knaup.koeln> wrote:
> 
> I also have no preference yet so I'll just throw in some thoughts.
> 
> ** Existing Code **
> The removal of the ternary operator would likely affect a lot of existing code.
> A quick search for " ? " (with spaces) over a large app of our team yields 304 results.
> 
> Two simpler examples:
> 
> [
>     "With Conditions":            hasReport ? "yes" : "no",
>     "With Image":                 hasImage ? "yes" : "no",
>     "With Message":               hasMessage ? "yes" : "no",
>     "Shared on Facebook Profile": sharedOnFacebookProfile ? "yes" : "no",
>     "Shared in Facebook Group":   sharedOnFacebookGroup ? "yes" : "no",
>     "Shared on Facebook Page":    sharedOnFacebookPage ? "yes" : "no"
> ]
> 
> view1.alpha = editing ? 1 : 0
> view2.alpha = editing ? 1 : 0
> view3.alpha = editing ? 0 : 1
> view4.alpha = editing ? 1 : 0
> 
> I am not sure using if…then…else would make this better to read & understand or worse.
> 

there seems to be a lot of people who dislike ternary operators. Other languages also are similar in dumping ternary. 

> 
> ** Keyword then **
> Making then a keyword would also cost us another word so that change needs to be carefully considered.
> In our large app I found just a single instance where then was used for a variable's name:
> 
> func reloadConfigurationAndThen(then: () -> Void) { … }
> Promises use the word then rather extensively: https://promisesaplus.com <https://promisesaplus.com/>
> 

Good point. Will think about it.

> On Sun, Dec 13, 2015 at 2:45 PM, Matthew Johnson via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> I'm not quite sure how I feel about this specific proposal yet but in general I do want to see conditional expressions and removal of the ternary operator.
> 
> I would like to see "else if" included in whatever we adopt as the final solution.  Is there a reason this is omitted from this proposal?  I apologize if that was discussed in the thread.  I haven't followed every post. 
> 
> Sent from my iPad
> 
> On Dec 12, 2015, at 11:54 PM, Paul Ossenbruggen via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
>> Hello All, 
>> 
>> Been sick in bed all day, but decided to try to be productive…
>> 
>> I did a rough draft of a proposal for implementing if expressions and switch expressions based upon the discussions we had here. I have tried to keep the scope of the changes as small as possible,  only added one keyword and kept things as similar to the existing language constructs as possible. If anyone wants to help me with this, or has feedback, please let me know,
>> 
>> https://github.com/possen/swift-evolution/blob/master/0020.md <https://github.com/possen/swift-evolution/blob/master/0020.md>
>> 
>> Thanks,
>> - Paul
>> 
>> 
>> 
>>> On Dec 12, 2015, at 3:51 PM, Paul Ossenbruggen <possen at gmail.com <mailto:possen at gmail.com>> wrote:
>>> 
>>> Implied in using the  “then", if…then…else would aways require “else" when using “then” similar to how “guard" requires “else”. This  will help to make the difference between statements and expressions clear.
>>> 
>>> let x = If cond then X else Y
>>> 
>>> is the full form, where “else" can not be omitted. 
>>> 
>>>> On Dec 12, 2015, at 12:59 PM, Paul Ossenbruggen <possen at gmail.com <mailto:possen at gmail.com>> wrote:
>>>> 
>>>> 
>>>> 
>>>>> On Dec 12, 2015, at 12:37 PM, Andrey Tarantsov via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>>>> 
>>>>> 1. I would really hate to explain to someone when if needs a then and when it doesn't. That's the sort of inconsistency that shouldn't be added lightly.
>>>> 
>>>> agreed definitely want to be careful with that. I think with braces meaning statements that differentiation can be made clear. I would certainly start with statements when describing, just as you usually don’t talk about the ternary operator until later. 
>>>> 
>>>>> 3. If we can somehow solve all of this, I think I'll be +1 for replacing (A ? B : C) with some sort of (if A then B else C).
>>>> 
>>>> Yes that would be great.
>>>> 
>>>>> 
>>>>> 4. Generally, I wonder how hard would it be for all statements to be usable as expressions? Why didn't Swift go that way from the start?
>>>> 
>>>> The biggest problem statement is you don’t need to exhaustively specify every outcome:
>>>> 
>>>> if cond {
>>>> 	print(“hello”)
>>>> }
>>>> 
>>>> whereas in an expression you have to specify what happens in the else.
>>>> 
>>>> let say = if cond then “hello” else “goodbye"
>>>> 
>>>> unless you go seriously off the deep end:
>>>> 
>>>> let say = if cond then “hello” 
>>>> 
>>>>  “say" then becomes an optional, *shudder*
>>>> 
>>>> 
>>> 
>> 
>> 
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