[swift-evolution] [Pitch] Removing Setter/Observer Name Overrides

[Jean-Daniel]

Of course, I meaned

 set(newValue foo: valueType) {

}

> Le 4 déc. 2016 à 09:56, Jean-Daniel via swift-evolution <swift-evolution at swift.org> a écrit :
> 
> If you want to go to the side of consistency, why not just require the standard method syntax like any other place ?
> 
> set(foo newValue: valueType) {
> 
> }
> 
> So old/newValue will become a parameter label.
> 
> 
>> Le 4 déc. 2016 à 04:06, Erica Sadun via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> a écrit :
>> 
>> [Original pitch: https://gist.github.com/erica/f5c58c689a6f479606c6158077c1962b <https://gist.github.com/erica/f5c58c689a6f479606c6158077c1962b>]
>> 
>> GENERAL FEEDBACK
>> 
>> I received a gratifying amount of feedback about my pitch here, on Twitter, 
>> through email, on several Slack channels, and on IRC. I wanted to summarize 
>> the feedback, to start a new round of discussion.
>> 
>> * A majority of respondents believe the current feature is incorrectly designed 
>>   and that this is our best opportunity to change it.
>> * A majority of respondents disagree on *how* it should be changed.
>> 
>> Before I commit to the (non-trivial) effort of pushing on this, I'd like to know if any 
>> of the core team can chime in on the "preferred" design. Thank you.
>> 
>> BUG REPORT
>> 
>> The notion that the compiler should check for `set(oldValue)`, `willSet(oldValue)`, 
>> and `didSet(newValue)` and emit warnings or errors had pretty much  universal
>> support. I have submitted https://bugs.swift.org/browse/SR-3310 <https://bugs.swift.org/browse/SR-3310> to address
>> this, regardless of whether the syntax changes or not.
>> 
>> MENTIONING NAMES
>> 
>> A majority of respondents prefer that argument names always be mentioned, 
>> whether or not they *can* be omitted. Consensus is that it's unSwifty
>> to use pre-built `newValue` and `oldValue` arguments without mentioning
>> them first.
>> 
>> * The current system violates the principle of clarity. 
>> * It adds too much magic (https://en.wikipedia.org/wiki/Magic_(programming)) <https://en.wikipedia.org/wiki/Magic_(programming))> 
>>   at the point of use. 
>> * It is inconsistent with the binding of variable names in closures.
>> 
>> My original design, which I chose to provide the least impact on the compiler and 
>> existing code, was the least popular option.
>> 
>> PREFERRED DESIGN
>> 
>> The most popular design is that setters and property observers follow closures
>> syntax,  namely that the old value and new value arguments be passed as $0, 
>> and assignable using `name in`. Under this design, a setter looks like:
>> 
>> ```
>> set { newValue in ... } // or
>> set { somethingElse in ... } // or
>> set { use $0 here }
>> ```
>> Swift loses the "magic" newValue and oldValue, but any developer who
>> normally prefers to mention the name before use has a simple, visible
>> and easy way to retain that clarity. 
>> 
>> * Mirrors closure syntax
>> * Easy to use
>> * Loses magic names
>> * Encourages documenting names in context
>> 
>> "NO CHANGE"
>> 
>> The second most popular design is "leave things as they are" (but implement the bug
>> report.) Developers with good style habits will use mandatory `newValue` and `oldValue`
>> names in their setter and observer declarations. No proposal is needed, and the bug
>> report guards against potential errors.
>> 
>> I would appreciate knowing whether the core team feels that the support for "no change",
>> even from a smaller group of developers, disqualifies this issue from the high bar of Phase 1.
>> 
>> (This group also included the most developers who self-reported that they did not
>>  use the override feature.)
>> 
>> REMOVING OVERRIDES
>> 
>> A third design entirely loses the ability to override variables or mention their names. 
>> This was in fact my *original* original design that I did not submit after sufficient 
>> devs told me they wanted to always spell out magic argument names. 
>> 
>> RIGHT NAMES ONLY
>> 
>> Finally, the least popular design is my original pitch. (Only allow the "right" names,
>> and allow them to be omitted.) This design has the least impact on the language, 
>> causes the least breaking for most use-cases, and allows most pro coders to continue
>> using the "mention all names" approach.
>> 
>> UPDATING PROPOSAL
>> 
>> I am happy to update the proposal for the "closure-like" design. I believe there *was*
>> reasonable consensus that the current system is out of step with Swift's design goals
>> to push forward. However, I want this to go through another round of feedback.
>> 
>> Thank you in advance for your comments. If this does move forward to a proposal, it
>> must be discussed and decided in the first phase of Swift 4 as the change *is* breaking.
>> 
>> -- Erica
>> 
>> 
>>> On Dec 1, 2016, at 10:22 PM, Derrick Ho <wh1pch81n at gmail.com <mailto:wh1pch81n at gmail.com>> wrote:
>>> 
>>> I like this proposal!
>>> 
>>> +1
>>> 
>> 
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