[swift-users] Problem with Access Control and Extensions

Adrian Zubarev adrian.zubarev at devandartist.com
Wed Sep 20 15:13:15 CDT 2017

I don’t get your problem here. If you don’t want to debate the correctness of your code, why are you asking for help or even showing error messages for a code snippet that cannot work?

1. Drop the access modifier from the extension itself, because this is only for convenience, which may or may not rule over the members of the extension members. If you’re already explicitly setting the access modifier on the extension members then the convenience access modifier makes no sense.
2. The code cannot work, because you cannot override `viewDidLoad` on a class that you don’t own, on a subclass of `UISplitViewController` that would be possible.

class MySplitViewController : UISplitViewController {}

extension MySplitViewController {
	override open func viewDidLoad() {
		/* ... */

Am 20. September 2017 um 21:41:31, Rick Aurbach via swift-users (swift-users at swift.org) schrieb:

I am trying to write an extension to a UIKit class, but am running into a can’t-win situation:

The code I ‘want’ to write looks like:

public extension UISplitViewController {
override public func viewDidLoad() {
if UIDevice.current.userInterfaceIdiom == .pad {
preferredDisplayMode = .automatic
} else {
preferredDisplayMode = .primaryOverlay

This generates the error message 
/Users/rlaurb/Projects/Cooks-Memory/Cooks-Memory/AppDelegate.swift:131:23: Overriding instance method must be as accessible as the declaration it overrides
/Users/rlaurb/Projects/Cooks-Memory/Cooks-Memory/AppDelegate.swift:131:23: Overridden declaration is here (UIKit.UIViewController)

But I can’t change the access control of the function to ‘open’, because I get the warning that the function can’t be “more” accessible than the extension.

And I can’t change the extension’s access to ‘open’ because apparently extensions can’t be open.

Now I don’t want to get into a debate about whether this code works — it’s just an experiment — but is it even possible to express this idea?? I.e., is it possible to express this idea without subclassing?


Rick Aurbach

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