[swift-evolution] Objective-C’s @compatibility_alias => Swift’s typealias?

Douglas Gregor dgregor at apple.com
Thu Jun 30 22:08:55 CDT 2016

> On Jun 30, 2016, at 3:16 PM, Ayaka Nonaka via swift-evolution <swift-evolution at swift.org> wrote:
> Hi Swift community,
> I was wondering if bridging Objective-C’s @compatibility_alias to Swift’s typealias is something that we have considered adding support for.
> For example, @compatibility_alias is useful for things like adding an alias like DCColor for UIColor and NSColor depending on the target. Here’s an example from our codebase:
> // For color compatibility, we alias DCColor to the appropriate class
> #import <UIKit/UIKit.h>
> @compatibility_alias DCColor UIColor;
> #else
> #import <Cocoa/Cocoa.h>
> @compatibility_alias DCColor NSColor;
> #endif
> We expected DCColor to be exposed to our Swift code, but it turns out that it is not. I’d imagine that we’re not the only ones using @compatibility_alias for similar things and other things that are useful. It would be really cool to see seamless bridging between @compatibility_alias and typealias, especially since we’ve seen a lot of other great backwards compatibility features in Swift 3.0 like importing lightweight-generics and #keyPath.

It definitely makes sense for @compatibility_alias to map to ‘typealias’, and I’d consider it a bug fix that doesn’t need a proposal. Thanks for bringing this up! I had no idea anyone knew about or used @compatibility_alias...

	- Doug

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