[swift-evolution] [discussion] Change the behavior of @objc on a class?

Charlie Monroe charlie at charliemonroe.net
Mon Jun 27 23:56:21 CDT 2016

Do you know how would this affect e.g. XIB files or CoreData models where you have the class name + module? If the class was previously marked @objc and now it would be implicitely @objc(ClassName), would it require all XIB files to be updated, or would the XIB compiler be able to deal with it? If the former, than it's a big no for me.

I'm not a big fan of a change on any account either, though, since it's absolutely not clear that @objc would have this side-effect.

> On Jun 27, 2016, at 10:26 PM, Jordan Rose via swift-evolution <swift-evolution at swift.org> wrote:
> Hey, all. An engineer at Apple noticed the following behavior:
> 1. class Foo: NSObject → exposed to Objective-C, Swift-style (mangled) runtime name
> 2. @objc class Foo: NSObject → exposed to Objective-C, Swift-style (mangled) runtime name
> 3. @objc(Foo) class Foo: NSObject → exposed to Objective-C, unmangled runtime name
> (and 4. @objc class Foo → illegal, classes must have ObjC heritage to be @objc.)
> They specifically observed that (1) and (2) have the same behavior, and suggested that maybe (2) should be shorthand for (3).
> Pros:
> - There aren't two ways to spell (1).
> - Removing the mangling (and module uniquing) from the runtime name is probably one of the most common uses of @objc on a class.
> Cons:
> - It's a source-breaking change, for all that the "@objc" in (2) is redundant.
> - For protocols, (1) and (2) are not equivalent, because @objc isn't inherited there.
> - Mangling is used to namespace class names at run time; if you drop that, the ObjC name should probably have a prefix. (This applies more to frameworks than apps, though.)
> There are probably people who say that last con applies to the generated header as well: we shouldn't put (1) or (2) into the generated header because the ObjC name might conflict with another class at compile time. This is valid, but probably too drastic a change at this point.
> So, what does everyone think? I'm leaning towards "no change" because it's a bit subtle and not a big enough win, but if there's widespread support for this I'll pull it into a proposal.
> Jordan
> P.S. This is rdar://problem/22296436 <rdar://problem/22296436> for anyone else at Apple.
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