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

[Radosław Pietruszewski]

This is very much on purpose. In more weakly typed languages, nil is treated as a “falsy” value, and so you can use || to deal with it. Swift is very strongly typed and only booleans can be used in boolean expressions, not boolean-like values. (Remember how you used to be able to do `if someOptional`, but it was changed so that you have to say `if someOptional != nil`). When we talk about optionals, we use ? symbol to convey that something is optional-related. And so there’s ??.

— Radek

> On 16 Feb 2016, at 15:18, James Campbell via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Granted it may be confusing since other languages use the Or operator which reads better.
> 
> X ||= y
> 
> However I would argue that this operator has no choice but to use ??= Since it is a mirror for the ?? Operation.
> 
> Perhaps it would be better for the language if ?? Was actually || but this would be a small but big change and would belong in another proposal.
> 
> Sent from Supmenow.com <http://supmenow.com/>
> 
> 
> 
> On Tue, Feb 16, 2016 at 6:14 AM -0800, "Ross O'Brien via swift-evolution" <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> 
> "y is assigned to x if x is nil" is exactly what "x ??= y" means. If x is nil, x is assigned the value of y; if x is not nil, it doesn't matter what y is.
> 
> This is exactly consistent with the boolean operator ||= ; "x ||= y" means "y is assigned to x if x is false" - if x is false, x is assigned the value of y; if x is true, it doesn't matter what y is.)
> 
> Why do you think it means the opposite?
> 
> On Tue, Feb 16, 2016 at 1:24 PM, David Sweeris via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
> -1, because in my mind, "x ??= y" kinda looks like "y is assigned to x iff y isn't nil", or, if you associate the ?? part with the lhs, "y is assigned to x if x is nil", neither of which is what the proposed operator means. In fact, the 2nd case is the *opposite* of what ??= means in this proposal.
> 
> To be clear, it's the syntax that I'm opposed to, not the concept.
> 
> - Dave Sweeris
> 
> On Feb 12, 2016, at 23:15, Douglas Gregor <dgregor at apple.com <mailto:dgregor at apple.com>> 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 <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 <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 <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 <https://github.com/apple/swift-evolution/blob/master/process.md>
>> Thank you,
>> 
>> Doug Gregor
>> 
>> Review Manager
>> 
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