[swift-evolution] ternary operator ?: suggestion

[Charles Constant]

Alex,

We know, from the traditional ternary, that a colon is going to satisfy the
requirements of a separator, even when we want to chain.

Is this the case with bar "|"? To me, this doesn't bode well....

let a = b ?
    2 : 3 |
    4 : 5 |
    _ : -1

Above, are we talking about a result of "3 [Bitwise OR] 4" or is the result
"3 [SEPARATOR] 4"? I could be wrong, but I suspect in practise, it would be
complicated to use, and probably not possible to chain.




On Wed, Jan 6, 2016 at 9:10 PM, Alex Popov <hello at alexpopov.ca> wrote:

> I like the bar `|` variation, but I do think the control value should be
> out front, otherwise the ? reads as an optional to my mind, whereas the
> former comes across as the beginning of a ternary (which this is
> effectively an extension of).
> The bar variation feels Haskell-y in a satisfying way, and also has the
> added benefit of clearly delimiting the effective "range" of the multiary.
>
> Alex Popov Jr.
> Principal iOS developer | Shelfie
> www.shelfie.com | @getshelfie
>
>
>
>
> On Wed, Jan 6, 2016 at 8:35 PM -0800, "Paul Ossenbruggen via
> swift-evolution" <swift-evolution at swift.org> wrote:
>
> Hi Charles,
>>
>> Chris, already said he did not like ? being used for ternary because it
>> was already used for optionals. I think because of historical precedent it
>> may be acceptable here.  I have tried combos earlier with ! and got no
>> support, admittedly not with the same usage as yours.
>>
>> Do you really find it confusing not having a separator there? It is
>> essentially a switch case without the word “case”. In my model the colon
>> only indicates the “else” or “default” case, the other cases are separated
>> by commas or whitespace. With my email taking the Swift Book examples and
>> converting it from statement to expression form, I did not find any of them
>> confusing, well maybe the first one, which found vowels and consonants, but
>> that did not look that great in statement form either. .
>>
>> if so maybe the | would be better as the separator because it would not
>> change the switch like syntax:
>>
>> let numberSymbol: Character = "三"  // Simplified Chinese for the number 3
>> let possibleIntegerValue:Int? = numberSymbol ?
>>    | "1", "١", "一", "๑": 1
>>    | "2", "٢", "二", "๒": 2
>>    | "3", "٣", "三", "๓": 3
>>    | "4", "٤", "四", "๔": 4
>>    |  _ : nil
>>
>> if let integerValue = possibleIntegerValue {
>>     print("The integer value of \(numberSymbol) is \(integerValue).")
>> } else {
>>     print("An integer value could not be found for \(numberSymbol).")
>> }
>> // prints "The integer value of 三 is 3.”
>>
>> But I still don’t see it a necessary.  perhaps that would allow removal
>> of the parenthesis and I think this would get rejected as not looking very
>> Swift like. Also single line form which isn’t bad:
>>
>> * let val = color ? **.Red:** 0xFF0000 | **.Green:** 0x00FF00 | *
>> *.Blue:** 0x0000FF** | **_:** 0xFFFFFF*
>>
>> But still not sure the | adds that much.
>>
>> * let val = color ? **.Red:** 0xFF0000, **.Green:** 0x00FF00, * *.Blue:*
>> * 0x0000FF, * *_:** 0xFFFFFF*
>>
>> Or this is without the commas is still readable but maybe a little harder:
>>
>> * let val = color ? **.Red:** 0xFF0000 **.Green:** 0x00FF00 * *.Blue:*
>> * 0x0000FF * *_:** 0xFFFFFF*
>>
>> One other thing, I would still prefer the control value inside the brace
>> rather than out front, but I see that most people still want it out front
>> and since it would be a breaking change for ternary, I have kind of backed
>> off it but I think this is still clearer because the control value is not
>> floating out in front.
>>
>> * let val =  ?(color, **.Red:** 0xFF0000, **.Green:** 0x00FF00, *
>> *.Blue:** 0x0000FF, * *_:** 0xFFFFFF)*
>>
>> On Jan 6, 2016, at 7:06 PM, Charles Constant <charles at charlesism.com>
>> wrote:
>>
>> > I see what you are trying to do, because of the colon being both used
>> for switch cases and
>> > separators for the ternary and so there needs to be a new character for
>> each case.
>> > I am not sure that putting colons between each case is really necessary
>> though.
>>
>> Most of us (including you and I) like a form that starts with " let val =
>> condition ? " like the existing ternary. Let's say a proposal like that
>> gets accepted... I really believe "colons as separators" is the best idea
>> in the case. Otherwise, it gets pretty confusing.. we'll have the existing
>> ternary where a colon does one thing, and our new "extra ternary" where it
>> does something else.
>>
>> This is why I like colons (this won't make sense unless your email has
>> rich text to show the colors):
>>
>> * let val = color ? *
>> *.Red !**  0xFF0000 : *
>> *.Green !**  0x00FF00 : *
>>
>> *_ !**  0xFFFFFF*
>>
>> ... no syntax here different from the existing except the addition "
>> *.Red !* ". As for the exclamation... Swift already uses an exclamation
>> for a billion other things, which is unfortunate. But the same can be said
>> of "?" and that's already used in a "switch" without causing confusion.
>>
>> > To point 1: I agree it needs a new name, I came up with the “demux
>> expression”
>> > but maybe there is a better name.
>>
>> Has anyone suggested "multiary expression" yet? Seems in keeping with
>> "ternary"
>>
>>
>>
>>
>>
>>
>>
>>
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