[swift-evolution] Should we relax restriction on closing over outer scope in class declarations?

[Micah Hainline]

That's exactly what I'm suggesting, the class declaration could work similarly to a closure.

> On Dec 22, 2016, at 4:15 PM, Michael Ilseman <milseman at apple.com> wrote:
> 
> Are you asking for a class declaration to implicitly capture and extend the lifetime of local variables? That seems like something that’s better done explicitly. Perhaps it’s better to think about how to reduce the boiler plate code, e.g. better default initializers.
> 
> (this is of course, additive and beyond the current scope of Swift 4 phase 1 planning)
> 
>> On Dec 22, 2016, at 2:39 PM, Micah Hainline via swift-evolution <swift-evolution at swift.org> wrote:
>> 
>> Currently we allow declarations of a new class in local scope, but
>> nothing can be referenced from the outer scope. Thus this is illegal:
>> 
>> ```
>> func foo() {
>>  let widgetString: String = createWidgetString()
>>  class SimpleProvider: WidgetStringProvider {
>>     func provideWidgetString() -> String {
>>        return widgetString // Illegal, defined in outer scope
>>     }
>>  }
>>  doThingsWithWidget(provider: WidgetStringProvider())
>> }
>> ```
>> 
>> I'm trying to feel out the edges of this decision, and figure out why
>> exactly this isn't allowed now, and how we might want to relax this in
>> the future if possible. While not a common construct, it is a useful
>> one.
>> 
>> Obviously there are ways around it, very simple to create an init and
>> a private let and do something like this:
>> 
>> ```
>> func foo() {
>>  let widgetString: String = createWidgetString()
>>  class SimpleProvider: WidgetStringProvider {
>>     private let widgetString: String
>> 
>>     init(widgetString: String) {
>>        self.widgetString = widgetString
>>     }
>> 
>>     func provideWidgetString() -> String {
>>        return widgetString // now legal, references
>> SimpleProvider.widgetString
>>     }
>>  }
>>  doThingsWithWidget(provider: WidgetStringProvider(widgetString:
>> widgetString))
>> }
>> ```
>> 
>> That's boilerplate I don't want to write though, as it somewhat
>> detracts from the readability of the structure. I'm not super
>> interested in defending the concept of local class definitions itself,
>> it's already allowed in the language, I'm just interested in the
>> syntax limitation and where that line might be able to be redrawn.
>> _______________________________________________
>> swift-evolution mailing list
>> swift-evolution at swift.org
>> https://lists.swift.org/mailman/listinfo/swift-evolution
>