[swift-evolution] ternary operator ?: suggestion

[J. Cheyo Jimenez]

Pick is interesting but how do you chain more that one pick/from together?

I thought about just just dropping the if.

let result = bool then 1 else bool then 2 else 3

Or going back to the python style.

let result = 1 where bool else where bool 2 else 3

But you are right, can't beat just having two characters. Specially when
the Elvis operator is in every other major c based language.

Perhaps this is just a like ! as a negation character, once you learn the
differences then u are set for other languages as well.

It would be nice to be able to bind expressions so that the actual logic of
the ?: is not lost.

let result = if (long_boolexpresion,
                   longerBoolexoression,
                   anotherboolExpression )
                   $0 then "a" else $1 && $2 then "b" else "c"


On Tuesday, December 15, 2015, Paul Ossenbruggen via swift-evolution <
swift-evolution at swift.org> wrote:

> I think pick…from may address many of the negatives listed by Chris. with
> the if..then..else approach.
>
> The closest proposal I’ve seen is the “if cond then value1 else value2”
> syntax, however that has serious (IMO) problems:
>
>
> - It is substantially more verbose than ?:, so much so that it obscures
> the logic that was trying to be captured.  Simple things like this become
> swallowed in syntax:
>   let x = cond ? 4 : 8
>   let x = if cond then 4 else 8
>
>
> this suggestion would still be longer, you can’t beat 2 chars. It is
> shorter than if..then..else though. Not sure there are any good options
> that can beat the conciseness of the ternary without replacing it with more
> syntax.
>
> let x = pick cond from 4, 8
>
>
> - Because it looks like an if statement, people will end up writing it
> like:
>
> let x = if cond then
> some_long_expression
>    else
> some_other_long_expression
>
>
>  - it only accepts expressions, not statements.  The way it is flowed
> makes it look like a statement.
>  - It is now force indenting a lot, which just looks weird and isn’t
> precedented in Swift.
>
>
> By having a new keyword, we can define the format and there is no prior
> connotation with it.
>
>
> When this happens, we now have new problems:
>  - At a glance, it “looks” like an if statement, but it is semantically
> different.
>
>
> Since it is a new it will always look like something that handles
> expressions only.
>
> Also this pick…from statement can be extended to handle switch expressions
> as well. So it is consistent way to do different expressions based upon an
> input.
>
> Some downsides:
> new keyword
> no prior history with other programming languages.
>
>
> On Dec 15, 2015, at 4:31 PM, Paul Ossenbruggen <possen at gmail.com
> <javascript:_e(%7B%7D,'cvml','possen at gmail.com');>> wrote:
>
> Been thinking a bit:
>
> Perhaps a new expression is in order. “Pick” this has a form like this.
> Param is a selector  This only allows expressions
>
> It has two forms:
>
> To replace ternary:
>
> let x = pick val from "abc", "cdef"
>
> To replace switch expressions. The cases follows existing rules for switch
> cases.
>
> let y = pick val from cases .Red: 1, .Green: 2, .Blue: 3
>
> This keeps the notion of expressions and statements quite separate. It
> avoids syntax confusion. It reads clear. It is fairy concise. It uses a
> straight forward pattern for both forms of expression.
>
> - Paul
>
> On Dec 15, 2015, at 2:06 PM, Charles Constant via swift-evolution <
> swift-evolution at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-evolution at swift.org');>> wrote:
>
> +1 bigtime for the assignment via Switch proposal
>
> I think someone here made the argument, I can't remember who, that it
> would be confusing for beginners. I think exactly the opposite.
>
> Once a new programmer has learned how to write a normal Switch statement,
> they'll be able to "leverage" the same concept and map values using the
> Switch assignment. Some might even try it on their on own, through
> experimentation, to see if it will work. It's such a pleasant experience
> when you try something in a language that seems consistent with what you
> already know, and discover "cool, it works!"
>
> At the moment, the alternatives are, what, using a dict to map values?
> trying to shoehorn a corrsponding set of values into an enum? using the
> existing switch statement (pretty verbose in Swift, due to "let" scope
> etc)? In my own Swift code, I have encountered situations, frequently,
> where I wished I had an equivalent to a ternary condition that handled more
> than two values. Chaining multiple ternary conditions together is
> unreadable. This proposed Switch assignment expression would take care of
> that.
>
> Definitely has my vote!
>
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