[swift-evolution] Optional Setting

[James Campbell]

Can you guys give me tips on how to improve this PR
https://github.com/apple/swift-evolution/pull/63 first time writing a
proposal or anything to do with a language. Let me know if there are points
I missed.

On Wed, Dec 16, 2015 at 12:26 AM, James Campbell <james at supmenow.com> wrote:

> On second thoughts, I'm preparing one :)
>
> On Wed, Dec 16, 2015 at 12:24 AM, James Campbell <james at supmenow.com>
> wrote:
>
>> Cool would be happy for you to do it :)  if you time, almost night here
>> so :) but happy for you to quote me in the proposal.
>>
>>
>>
>> On Wed, Dec 16, 2015 at 12:17 AM, Jacob Bandes-Storch <jtbandes at gmail.com
>> > wrote:
>>
>>> Would there be any caveats in introducing something like this, given the
>>> raciness of the operator? I guess it's not really a big deal — the other
>>> compound assignment operators (+=, -=, etc.) have the same problem.
>>>
>>> I'm not hearing much argument; sounds like many are in favor. I'd be
>>> happy to flesh out my radar into a "??=" proposal this evening, or someone
>>> else can do it if they'd like.
>>>
>>> Jacob
>>>
>>> On Tue, Dec 15, 2015 at 4:12 PM, Jordan Rose <jordan_rose at apple.com>
>>> wrote:
>>>
>>>> It's possible that @_transparent
>>>> <https://github.com/apple/swift/blob/master/docs/TransparentAttr.rst> is
>>>> handled early enough in the compiler that we actually would get this
>>>> behavior. I'm not sure, though.
>>>>
>>>> +1 from me whether or not didSet is always called, though. "a = a ?? b"
>>>> always calls didSet anyway.
>>>>
>>>> Jordan
>>>>
>>>> P.S. There's nothing particularly useful in the Radar, except that
>>>> together with the dups there are three suggested spellings: "=?", "?=", and
>>>> "??=". My vote is with Brent for "??=".
>>>>
>>>> On Dec 15, 2015, at 15:26 , James Campbell via swift-evolution <
>>>> swift-evolution at swift.org> wrote:
>>>>
>>>> :) Wasn't expecting it to be trivial. but yeah if it could somehow be
>>>> short circuited so didSet, willSet isn't called when there is a value
>>>> already. that would be awesome.
>>>>
>>>> Could the willSet, didSet behaviour  be tied to the = behaviour ?  in
>>>> your example above the operation ultimately cascades into a = operation.
>>>>
>>>> Same with operations such as *= or /= ultimately it has to do a =
>>>> operation to set the new calculated value.
>>>>
>>>> On Tue, Dec 15, 2015 at 11:23 PM, Jacob Bandes-Storch <
>>>> jtbandes at gmail.com> wrote:
>>>>
>>>>> I agree that would be nice. Just pointing out that it's nontrivial. If
>>>>> you implement this custom operator today, you get different behavior.
>>>>>
>>>>> Jacob
>>>>>
>>>>> On Tue, Dec 15, 2015 at 3:21 PM, James Campbell <james at supmenow.com>
>>>>> wrote:
>>>>>
>>>>>> If it has a value already the nit wouldn't call anything as it
>>>>>> technically hasn't been set. Only if it already has a value does it try and
>>>>>> set something in which case the didSet is called :)
>>>>>>
>>>>>> On Tue, Dec 15, 2015 at 11:16 PM, Jacob Bandes-Storch via
>>>>>> swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>
>>>>>>> One possible caveat is with custom setters.
>>>>>>>
>>>>>>> If "a" already has a value, does "a ??= b" call the custom
>>>>>>> setter/willSet/didSet, or does it see the nil and short-circuit?
>>>>>>>
>>>>>>> This can be implemented today:
>>>>>>>
>>>>>>>     func ??=(inout lhs: T?, @autoclosure rhs: () -> T?) { if lhs ==
>>>>>>> nil { lhs = rhs() } }
>>>>>>>
>>>>>>> However, the use of "inout" will always cause the didSets to be
>>>>>>> triggered at the call site, when just using if-statements instead wouldn't
>>>>>>> have done so.
>>>>>>>
>>>>>>> Jacob
>>>>>>>
>>>>>>> On Tue, Dec 15, 2015 at 3:10 PM, Brent Royal-Gordon via
>>>>>>> swift-evolution <swift-evolution at swift.org> wrote:
>>>>>>>
>>>>>>>> > I think that the existing syntax for “??” handles this need
>>>>>>>> fairly well without requiring an additional assignment operator:
>>>>>>>> >
>>>>>>>> >       a = a ?? []
>>>>>>>>
>>>>>>>> When the variable is `a`, sure. When it’s
>>>>>>>> `scoreboardViewController.selectedScoreboard`, not so much.
>>>>>>>>
>>>>>>>> +1 from me, though I prefer the `??=` spelling to match the `??`
>>>>>>>> operator more closely.
>>>>>>>>
>>>>>>>> --
>>>>>>>> Brent Royal-Gordon
>>>>>>>> Architechies
>>>>>>>>
>>>>>>>> _______________________________________________
>>>>>>>> swift-evolution mailing list
>>>>>>>> swift-evolution at swift.org
>>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> swift-evolution mailing list
>>>>>>> swift-evolution at swift.org
>>>>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>>>>
>>>>>>>
>>>>>>
>>>>>>
>>>>>> --
>>>>>>  Wizard
>>>>>> james at supmenow.com
>>>>>> +44 7523 279 698
>>>>>>
>>>>>
>>>>>
>>>>
>>>>
>>>> --
>>>>  Wizard
>>>> james at supmenow.com
>>>> +44 7523 279 698
>>>>  _______________________________________________
>>>> swift-evolution mailing list
>>>> swift-evolution at swift.org
>>>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>>>
>>>>
>>>>
>>>
>>
>>
>> --
>>  Wizard
>> james at supmenow.com
>> +44 7523 279 698
>>
>
>
>
> --
>  Wizard
> james at supmenow.com
> +44 7523 279 698
>



-- 
 Wizard
james at supmenow.com
+44 7523 279 698
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