Hi Rick,
Unfortunately, that is the case. You cannot subclass a Swift class (even if it
is a subclass of NSObject and available to the Objective-C runtime) because of
deliberate limitations baked into Obj-C to block subclassing Swift classes in
Obj-C code.
I believe the reason for this limitation is that Swift includes features that
cannot be utilised in Obj-C and therefore subclasses would be restricted and
would get undefined behaviour when implementing methods that cannot cross into
Obj-C.
If Apple were to allow Obj-C -> Swift -> Obj-C subclassing, then it would be on
a limited basis. Some methods wouldn’t do the same thing in Swift as they would
in Obj-C selectors, and you could theoretically declare conflicting methods in
your subclass that would have different actions depending on whether you were
addressing the class in Swift and Obj-C. Additionally, the Swift Compiler
couldn’t see beyond the Swift barrier and therefore may make optimisations that
would break your Obj-C subclasses.
While I understand the frustration behind this, both in personal projects and
philosophically, I think that this is unfortunately the better of the two
options.
- Rod
> On 15 Apr 2017, at 12:41 pm, Rick Mann via swift-users
> <swift-users@swift.org> wrote:
>
> I'm refactoring some Objective-C code to inherit from a new Swift super
> class. This has been going okay, and I've been cleaning up build errors as I
> spot them (some auxiliary enums caused enum name changes, etc.).
>
> But my last error seems to be that I can't subclass the Swift class: "Cannot
> subclass a class with objc_subclassing_restricted attribute". I didn't notice
> it before, and all the online references that say you can't subclass a Swift
> class point to a Swift document that no longer mentions that. They also don't
> say what they mean by "Swift" class (e.g. is it not marked with @objc?).
>
> In any case, my Swift class looks like:
>
> @objc
> class
> Camera : NSObject
> {
> ...
> }
>
> And my ObjC class looks like:
>
> @interface
> MCPCamera : Camera
>
> ...
>
> @end
>
> I feel like this is a reasonable thing to try to do. Is it just not possible?
>
> --
> Rick Mann
> rm...@latencyzero.com
>
>
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