[swift-evolution] [Review] SE-0024 "Optional Value Setter `??=`"

[Ross O'Brien]

>       • What is your evaluation of the proposal?

I'm for the adoption of this operator.

Acknowledging previous comments: Swift values non-optional and immutable
types, but I don't see this operator as encouraging optionals or mutable
types; instead I see it as one step in the process of make clearer how
mutable optionals are used. They aren't going anywhere.

The difficulties of '??=' lie with '??', because it's overloaded; it serves
both of these signatures:
1) Optional<T> ?? Optional<T> -> Optional<T>
2) Optional<T> ?? T -> T
If we disambiguated this operator - for the sake of example, replaced the
operator in 1) with '???' and kept 2) as is - then '??=' would be
meaningless (its left argument would never be optional) and this proposal
would instead be for the inclusion of '???=', which would be unambiguous.
And the number of question marks alone would drown the developer in doubt
until they went for the straightforward non-optional constant others in
this thread feel this operator would encourage.

As a further suggestion: just as the Swift compiler will currently warn a
developer that a local variable is unused (and suggest replacing it with
'_') or that a variable doesn't change (and suggest replacing its
declaration with '??'), perhaps it could be possible to identify situations
where an optional var could be replaced with a non-optional let if a '??='
statement was rewritten as '??', and issue an appropriate warning.

>       • Is the problem being addressed significant enough to warrant a
change to Swift?

Swift encourages non-optionals. This isn't a significant problem,
particularly if one follows the law of Demeter as one codes. But it's a
nice addition.

>       • Does this proposal fit well with the feel and direction of Swift?

Yes. Swift will continue to have optionals, and code handling optionals
should be clear. As long as the meaning of ?? is clearly understood, ??=
will be.

>       • If you have used other languages or libraries with a similar
feature, how do you feel that this proposal compares to those?

I haven't used a similar feature in other languages, but have previously
wished for such an operator in Objective C (prior to its
nullable/nonnullable additions).

>       • How much effort did you put into your review? A glance, a quick
reading, or an in-depth study?

I've read the proposal and much of the swift-evolution discussion of it.

On Wed, Feb 17, 2016 at 5:47 PM, Tal Atlas via swift-evolution <
swift-evolution at swift.org> wrote:

> I think that overall this is a good operator that eventually should get
> in. At this point though the wins that this would bring are probably not
> worth the added complexity to the language.
>
> As Joe said the primary use case for the hammer operator `||=` in ruby is
> not even covered by this operator, so it’s use would be far more limited
> than in those languages.
>
> -Tal
>
> On Sat, Feb 13, 2016 at 12:15 AM, Douglas Gregor via swift-evolution <
> swift-evolution at swift.org> wrote:
>
>> Hello Swift community,
>>
>> The review of SE-0024 "Optional Value Setter `??=`" begins now and runs
>> through February 18, 2016. The proposal is available here:
>>
>>
>> https://github.com/apple/swift-evolution/blob/master/proposals/0024-optional-value-setter.md
>>
>> Reviews are an important part of the Swift evolution process. All reviews
>> should be sent to the swift-evolution mailing list at
>>
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>> or, if you would like to keep your feedback private, directly to the
>> review manager. When replying, please try to keep the proposal link at the
>> top of the message:
>>
>> Proposal link:
>>
>>
>> https://github.com/apple/swift-evolution/blob/master/proposals/0024-optional-value-setter.md
>>
>> Reply text
>>
>> Other replies
>>
>> <https://github.com/apple/swift-evolution#what-goes-into-a-review-1>What
>> goes into a review?
>>
>> The goal of the review process is to improve the proposal under review
>> through constructive criticism and, eventually, determine the direction of
>> Swift. When writing your review, here are some questions you might want to
>> answer in your review:
>>
>>    - What is your evaluation of the proposal?
>>    - Is the problem being addressed significant enough to warrant a
>>    change to Swift?
>>    - Does this proposal fit well with the feel and direction of Swift?
>>    - If you have used other languages or libraries with a similar
>>    feature, how do you feel that this proposal compares to those?
>>    - How much effort did you put into your review? A glance, a quick
>>    reading, or an in-depth study?
>>
>> More information about the Swift evolution process is available at
>>
>> https://github.com/apple/swift-evolution/blob/master/process.md
>>
>> Thank you,
>>
>> Doug Gregor
>>
>> Review Manager
>>
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>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>>
>>
>
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