[swift-evolution] ternary operator ?: suggestion

[Marc Knaup]

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.


** 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

On Sun, Dec 13, 2015 at 2:45 PM, Matthew Johnson via swift-evolution <
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> 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
>
> Thanks,
> - Paul
>
>
>
> On Dec 12, 2015, at 3:51 PM, Paul Ossenbruggen <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> wrote:
>
>
>
> On Dec 12, 2015, at 12:37 PM, Andrey Tarantsov via swift-evolution <
> 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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