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

[Douglas Gregor]

> On Jun 27, 2016, at 1:26 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.)

I’m -1 on this, because bare “@objc” in other contexts means “make sure this is exposed to Objective-C, but I don’t want to be explicit about the name” while “@objc(something)” means “make sure this is exposed to Objective-C, and ‘something’ is the name”. 

	- Doug


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