[swift-evolution] Setter methods for vars

[L. Mihalkovic]

Regards
(From mobile)

> On Jun 29, 2016, at 1:11 AM, Michael Peternell via swift-evolution <swift-evolution at swift.org> wrote:
> 
> Really?? Or we just have #set and #get and no lenses, and it's done for Swift 3?
> 
> I never heard of lenses (Google does not help here). Was this serious or were you joking?

http://days2012.scala-lang.org/sites/days2012/files/morris_lenses.pdf

Not a joke at all. Read first sentence for brief definition.

> Unless you can explain why #set and #get without lenses would be bad... or maybe #set and #get *are* lenses, in which case I'm not sure what you were trying to say. Reflexion -> Reflection?
> 
> -Michael
> 
>> Am 29.06.2016 um 00:55 schrieb David Hart via swift-evolution <swift-evolution at swift.org>:
>> 
>> This looks like lenses. I think we need to wait until after Swift 3 to discuss it, and come up with a bigger design that ties to reflexion.
>> 
>>> On 28 Jun 2016, at 22:04, Michael Peternell via swift-evolution <swift-evolution at swift.org> wrote:
>>> 
>>> So you're proposing that `#set(aVariableName)` should translate to `{aVariableName=$0}`, right? Where aVariableName can be any valid lvalue like `self.users` or `users` or `vc.viewControllers`..
>>> 
>>> I think this would be a good extension to Swift. (`users.set` does not work BTW, because maybe the `users` object has a `set` property.. maybe I wanted to refer to the `set` property which also happens to refer to a closure value.)
>>> 
>>> `#set(aVariableName)` also feels consistent with the `#keyPath(aVariableName)` property and falls into a similar category. Maybe `#setter(aVariableName)` would be even more clear? Furthermore, I want to additionally propose to introduce `#get(aVariableName)` (or `#getter(aVariableName)`) too.
>>> 
>>> -Michael
>>> 
>>>> Am 28.06.2016 um 20:18 schrieb Austin Feight via swift-evolution <swift-evolution at swift.org>:
>>>> 
>>>> Proposal:
>>>> 
>>>> I propose adding setter methods to vars, which could look something like this: `ApiClient().fetchUsers().then(#set(users))`
>>>> 
>>>> Initially I thought it should work like this: `ApiClient().fetchUsers().then(users.set)`
>>>> but to accomplish a line of code that flows grammatically, I believe putting "set" where it would naturally fall if the code was being read as a sentence is more Swifty.
>>>> 
>>>> Rationale:
>>>> 
>>>> The following code makes me smile:
>>>> 
>>>> ApiClient().fetchUsers().then(displayUsers)
>>>> 
>>>> It exemplifies the beauty of Swift. First-class functions make this line of code read very well. Consider some alternatives:
>>>> 
>>>> 1. ApiClient().fetchUsers().then { displayUsers($0) }
>>>> 2. ApiClient().fetchUsers().then { users in displayUsers(users) }
>>>> 3. ApiClient().fetchUsers().then { (users: [User]) in displayUsers(users) }
>>>> 
>>>> Using the lessons learned from Swift API Design Guidelines (WWDC 2016 Session 403) having an emphasis on clarity, my analysis of the alternatives is:
>>>> 
>>>> 1. $0 adds no additional information as to the type or explanation of what the argument is, thus adding nothing to the line of code for clarity, and therefore should be omitted
>>>> 2. adding "users" also adds nothing to the clarity of the code. The function, properly, contains the information necessary to reason about the argument it takes and what it does, and therefore adding "users" is redundant
>>>> 3. Not only is "users" redundant, but also is the explicit type label. The `displayUsers` method will only accept one type of argument, so we're duplicating information that the compiler (and autocomplete) already gives us
>>>> 
>>>> With this I conclude that `ApiClient().fetchUsers().then(displayUsers)` is the Swiftiest option.
>>>> I want to extend this same logic to when I find myself writing code like this:
>>>> 
>>>> ApiClient().fetchUsers().then { users in
>>>> self.users = users
>>>> }
>>>> 
>>>> or alternatively, because "users" is likely redundant information again,
>>>> 
>>>> ApiClient().fetchUsers().then { self.users = $0 }
>>>> 
>>>> Personally I steer clear of `$0` as much as possible, because I very rarely feel that it provides the information necessary for code clarity. But beyond that, this code no longer reads as nicely as the code we had before. 
>>>> 
>>>> Whereas `ApiClient().fetchUsers().then(displayUsers)` flows nicely as a sentence and reads grammatically, `ApiClient().fetchUsers().then { self.users = $0 }` no longer does.
>>>> 
>>>> I think this feature could have a simple implementation where the compiler replaces `#set(X)` with `{ X = $0 }`, and I believe it would go a long way with respect to code clarity, especially when X is something longer like `self.view.bounds.origin.x`
>>>> 
>>>> 
>>>> Looking forward to hearing thoughts from the community,
>>>> Austin Feight
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>>> 
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