[swift-evolution] [Further Discussion] Naming Attributes

[Joe Groff]

> On Feb 19, 2016, at 12:17 PM, Erica Sadun <erica at ericasadun.com> wrote:
> 
> > Here's a problem
> 
> * There are Swift attributes: @autoclosure, @available, @objc, @noescape, @nonobjc, @noreturn, @testable, @warn-unused-result, @convention, @noreturn.
> * There are ObjC-ish/Xcode-ish attributes: @UIApplicationMain, @NSManaged, @NSCopying, @NSApplicationMain, @IBAction, @IBDesignable, @IBInspectable, @IBOutlet
> * There may be user-definable attributes under SE-0030: for example @lazy, @delayed; these are certainly attribute-ish, and it makes sense to present these using attribute-syntax.
> * The attribute syntax using `@` has had an intention "to open the space up to user attributes at some point"
> 
> > Namespacing
> 
> If Swift were to start accepting user-defined attributes,  it would need some way to differentiate and namespace potential conflicts. The most obvious solution looks like this:
> 
> `@Swift.autoclosure`, `@UIKit.UIApplicationMain`, `@UIKit.IBOutlet`, `@Swift.noreturn`, `@Custom.lazy`, etc.
> 
> Cumbersome, ugly, problematic.
> 
> > Modernization
> 
> In my initial discussion for modernizing Swift attributes (https://gist.github.com/erica/29c1a7fb7f49324d572f <https://gist.github.com/erica/29c1a7fb7f49324d572f>), I wanted to eliminate snakecase from @warn-unused-result and `mutable_variant`. Of these, the second is a no-brainer. Instead of the non-standard argument label `mutable_variant`, use `mutableVariant`. Problem solved.
> 
> Converting `warn-unused-result` to the current standard of lowercase `warnunusedresult` produces a hard-to-read outcome. So in my write-up, I proposed the following amendments:
> 
> @Autoclosure // was @autoclosure
> @Available // was @available
> @ObjC // was @objc
> @NoEscape // was @noescape
> @NonObjC // was @nonobjc
> @NoReturn // was @noreturn
> @Testable // was @testable
> @WarnUnusedResult // was @warn-unused-result
> @Convention  // was @convention
> @NoReturn // was @noreturn
> 
> This was greeted somewhere between warmly and Siberian Winter depending on respondent. 
> 
> > Possible Approaches
> 
> After reading through Joe Groff's update to SE-0030, I'd like to push this again in a broader context (which is why I'm starting a new email thread). 
> 
> * Is traditional namespacing the way to go? 
> * Could a simpler solution to upper camel all system-supplied attributes and lower camel all custom attributes be sufficient?
> * Could any other "custom" decoration differentiate the two with easy parsing: for example @@lazy, @@delayed for custom and single-@ tokens for system supplied?
> * Should I simply back off on modernizing warn-unused-result until SE-0030 is resolved?
> 
> What are your thoughts?

Once we open the floodgates for user-defined attributes, I think traditional namespacing and name lookup makes a lot of sense. We could conceptually namespace the existing hardcoded attributes into appropriate modules (Swift for the platform-neutral stuff, Foundation/AppKit/UIKit as appropriate for Appley stuff); name collisions would hopefully be rare enough that "@Swift.AutoClosure" or whatever hopefully won't often be necessary.

-Joe
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