[swift-users] protocols, optional, and public

[Zhao Xin]

>
> “Optional requirements are available so that you can write code that
> interoperates with Objective-C. Both the protocol and the optional
> requirement must be marked with the @objc attribute. ”
>


from: Apple Inc. “The Swift Programming Language (Swift 3 Beta)”。 iBooks.
> https://itun.es/us/k5SW7.l


I think the  CLLocationManagerDelegate you saw was converted from
Objective-C, which means it was not written in Swift directly. It was just
the counterpart called interface. In swift, interface is automatically
generated. It is not the source file.

For example, you can create a new project, open a swift file, open
assistant window (option+command+enter). Add a protocol in your swift file.

public protocol UnmanagedCopy {
>     func unmanagedCopy() -> Self
> }


Build your project. Reload your interface file in the assistant window by
changing to other files and back. You can see the counterpart is

public protocol UnmanagedCopy {
>

    public func unmanagedCopy() -> Self
> }


You should aware that though there is a `public func` in interface. You can
not do it in protocol definition in source file.

Further more, I also test a new protocol Foo.

@objc public protocol Foo {
>     @objc optional func bar()
> }


It turns out the counterpart is not as my expectation. The @objc remains.

 @objc public protocol Foo {
>     @objc optional public func bar()
> }


Since my testing code was written in Swift, I thought the reason of that
was because the interface generated from Objective-C code was not identical
as from Swift. For an interface file generated from Objective-C, the source
code was definitely working in Objective-C. So the interface file was for
Swift only, which means there was no need to apply those restrictions.

Zhaoxin

On Sat, Aug 27, 2016 at 8:52 AM, Rick Mann via swift-users <
swift-users at swift.org> wrote:

> I'm wrapping CLLocationManager (and its delegate), and I'm trying to
> create a protocol like this. This is directly cribbed from
> CLLocationManagerDelegate.
>
> ---------------
> public
> protocol
> LZLocationManagerDelegate : NSObjectProtocol
> {
>     optional public func locationManager(manager: LZLocationManager,
> didUpdateLocations locations: [CLLocation])
> }
> ---------------
>
> But I get these errors:
>
> LZLocationManager.swift:16:5: 'optional' can only be applied to members of
> an @objc protocol
> LZLocationManager.swift:70:41: Cannot use optional chaining on
> non-optional value of type '(LZLocationManager, didUpdateLocations:
> [CLLocation]) -> ()'
>
> Apple's version compiles flawlessly (comments removed):
>
> ---------------
> public protocol CLLocationManagerDelegate : NSObjectProtocol {
>     @available(iOS 6.0, *)
>     optional public func locationManager(manager: CLLocationManager,
> didUpdateLocations locations: [CLLocation])
>
>     // ...remainder removed for brevity
> }
> ---------------
>
> Adding @objc fixes it, but I would have thought NSObjectProtocol implied
> that. Also, when I look at the Apple Swift exports, it's not there (is that
> a limitation of the exported view?).
>
> --
> Rick Mann
> rmann at latencyzero.com
>
>
> _______________________________________________
> swift-users mailing list
> swift-users at swift.org
> https://lists.swift.org/mailman/listinfo/swift-users
>
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