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

Thorsten Seitz tseitz42 at icloud.com
Wed Feb 17 11:03:51 CST 2016

-1 to the proposal.

Kevin and others have summed up the reasons already: the operator is encouraging mutability and optionality where it would not be needed and using it therefore seems to be an anti pattern. 


> Am 17.02.2016 um 06:26 schrieb Kevin Ballard via swift-evolution <swift-evolution at swift.org>:
>> On Fri, Feb 12, 2016, at 09:15 PM, Douglas Gregor wrote:
>> What is your evaluation of the proposal?
> -1. If we were to have this operator, then I think `??=` is a good choice for it. But I don't think we need this operator. As others have pointed out, a lot of the use-cases from other languages don't actually work in Swift, and having the operator encourages people to write anti-patterns in order to use it, such as making a value into a mutable Optional when it really should be an immutable non-optional value.
>> Is the problem being addressed significant enough to warrant a change to Swift?
> No. The need for this sort of operator is much rarer in Swift than it is in languages that do have an equivalent (like Ruby).
> Anecdotally, I've written a lot of Swift code at this point, and I've never wanted this. I have on rare occasion wanted a local "lazy" variable, but in those rare instances, the desire was to move the initialization out of the main body of the function and up to the declaration, which `??=` doesn't help with.
>> Does this proposal fit well with the feel and direction of Swift?
> The choice of operator I think is reasonable, given the existing `??` operator, but encouraging the use of Optionals for local variables that will end up with a guaranteed-non-Optional value does not.
>> If you have used other languages or libraries with a similar feature, how do you feel that this proposal compares to those?
> The only languages that I know of with a similar operator also return the rhs value from the assignment expression, and that's not something Swift would do. So this is less useful than the operator in those languages.
>> How much effort did you put into your review? A glance, a quick reading, or an in-depth study?
> A quick reading.
> -Kevin Ballard
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