[swift-evolution] Proposal: Replace ?? by an (optional) argument to ?

[Ross O'Brien]

What about it?

"x ?? false" is simple. If x isn't nil, return x; if x is nil, return false.
"x?.isEmpty ?? false" again is already readable; if x isn't nil, return
x.isEmpty; if x is nil, return false.

"Bool(x?.isEmpty)" seems be suggesting that the Bool type has a failable
initialiser "init?(_: Bool?)". If x is nil, x.isEmpty would be nil, so the
resulting Bool would be nil, not false - this code returns a Bool?, which
you already had.

"??(false, x?.isEmpty)" ... uses an operator as an identifier, for a start.
At best I'd try to interpret this like reduce - take a collection or
variadic list of optionals, return the value of the first non-nil else
return the "default". Except I'd still put the default at the end, because
I can't think why it would be at the start.

So, if the given problem is taking the nil-coalescing and putting it up
front, perhaps there should be a global generic function:

func firstNonOptional<T>(possibles:T?..., failsafe:T) -> T
{
    return possibles.reduce(nil, combine:{ $0 ?? $1 }) ?? failsafe
}



On Fri, Jan 29, 2016 at 1:48 PM, Amir Michail via swift-evolution <
swift-evolution at swift.org> wrote:

>
> On Jan 29, 2016, at 8:42 AM, Craig Cruden <ccruden at novafore.com> wrote:
>
> still much worse.
>
>
> What about: Bool(x?.isEmpty) // nil and false => false
>
>
> On 2016-01-29, at 20:41:06, Amir Michail via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> On Jan 29, 2016, at 5:03 AM, Thorsten Seitz <tseitz42 at icloud.com> wrote:
>
> I agree with Erica. The ?? operator is very readable IMO.
>
> Furthermore x?(false).isEmpty looks like it would evaluate false.isEmpty
> when x is nil which is certainly not what is intended.
>
>
> What about this then: ??(false, x?.isEmpty)
>
> In addition it would not be clear which default should be used in case of
> multiple optional chainings happening, i.e. what should be the result of
> person?(false).address?.(true).isEmpty
>
> -Thorsten
>
>
> Am 26. Januar 2016 um 03:29 schrieb Erica Sadun via swift-evolution <
> swift-evolution at swift.org>:
>
> Not loving this. I'm quite happy with ??-coalescing and don't see
> a compelling reason it needs to be "cleaner". I find your suggested
> enhancement less readable. Looks like an optional chaining across
> a function.
>
> -- E
>
> On Jan 25, 2016, at 7:03 PM, Amir Michail via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>
> Examples:
>
>
> * instead of x ?? false, you would have x?(false)
>
> * instead of x?.isEmpty ?? false, you would have x?(false).isEmpty
>
>
> I think this change would result in cleaner looking code.
>
>
>
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