[swift-evolution] ternary operator ?: suggestion

Charles Constant charles at charlesism.com
Tue Jan 5 01:16:34 CST 2016

Thanks Austin,

*let myThing = {*
*  if someCondition {*
*    return 1*
*  } else {*
*    return 2*
*  }*

While that is ugly, it does have the benefit of being crystal clear about
its intent (i.e.: setting "myThing") since everything after the first line
is going to be indented.

What I dislike about using a "switch" to achieve the same thing is
rereading my code. It can take a couple moments to clue in that its just
assigning, and to realize there's nothing *else* going on in the "switch"
aside from the assignment.

On Mon, Jan 4, 2016 at 11:04 PM, Austin Zheng <austinzheng at gmail.com> wrote:

> There was a popular pattern which went as follows:
> let myThing = {
>   if someCondition {
>     return 1
>   } else {
>     return 2
>   }
> }()
> It's a little ugly, but the compiler is apparently smart enough to
> inline/optimize away the anonymous closure. It became less popular once
> Swift got support for declaring lets without an initial value.
> Austin
> On Jan 4, 2016, at 10:55 PM, Charles Constant via swift-evolution <
> swift-evolution at swift.org> wrote:
> My best guesses here, since I didn't write and don't entirely agree...
> *> Please detail what the trade offs are*
> Other than more complexity, I think this refers to making the "switch"
> statement do two slightly different things. Of course, if we call it
> something else, like "match" or "which" then it stops being an issue.
> *> What are the other ways that Swift currently supports this?*
> As far as I can see, the closest we get are...
>     a) The existing "switch" statement, or if else statement (preceded
> with a statement to declare the variable. yuck). I think this is verbose
> enough to qualify as "confusing"
>     b) Creating an anonymous dict, and immediately accessing it (which
> means the keys need to be Hashable). This isn't very flexible
>     c) Creating a special init or function, to map one enum, to another.
> This  is also verbose, and not flexible, and moves the code away from where
> it used (even if you never reuse the mapping).
>     d) Chaining a bunch of conditions in a ternary... Horrible.
> Anyone know of any better alternatives? It feels like I'm missing
> something.
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