# AnyObject parameter: "Cannot assign to immutable expression" **URL:** \ **Category:** Using Swift\ **Created:** [October 3, 2018, 12:45am UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642 "2018-10-03T00:45:58Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![pkamb](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/pkamb/32/2500_2.png) [@pkamb](https://forums.swift.org/u/pkamb)\ **Post date:** [October 3, 2018, 12:45am UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642/1 "2018-10-03T00:45:58Z")
I'm hitting this issue in my `NSOpenSavePanelDelegate` in a Sandboxed Mac app. [https://developer.apple.com/documentation/appkit/nsopensavepaneldelegate/1527117-panel](https://developer.apple.com/documentation/appkit/nsopensavepaneldelegate/1527117-panel) I need to get a reference to the sender as a Panel and set the directory. ```swift /* NSSavePanel/NSOpenPanel: Gets and sets the directoryURL shown. */ @available(OSX 10.6, *) open var directoryURL: URL? ``` All of my `as?` casts fail because the Sandbox uses a private subclass for these items. If I use AnyObject, Xcode autocomplete suggests the correct method as suggested here: > But for some reason the variable is marked as immutable, and thus I cannot actually set any properties...? ``` extension PanelController: NSOpenSavePanelDelegate { func panel(_ sender: Any, didChangeToDirectoryURL url: URL?) { // Sandboxed app; PowerBox open/save panels // sender is `NSVBOpenPanel` and/or `NSKVONotifying_NSVBOpenPanel` // but I cannot `as?` cast to those private classes var panel = sender as AnyObject // ERROR: "Cannot assign to immutable expression of type 'URL??'" panel.directoryURL = URL(fileURLWithPath: "/")! // ERROR: "Cannot assign to immutable expression of type 'URL?'" panel.directoryURL? = URL(fileURLWithPath: "/")! } } ``` Any suggestions for getting past this error or getting a reference to the Panel? ---
**Author:** ![jrose](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/jrose/32/408_2.png) [@jrose](https://forums.swift.org/u/jrose)\ **Post date:** [October 3, 2018, 1:02am UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642/2 "2018-10-03T01:02:48Z")
This is a longstanding bug, but it looks like we don't have a JIRA bug for it. Inside Apple it's \ "Cannot assign to a property through AnyObject", and it's very similar to [SR-5475](https://bugs.swift.org/browse/SR-5475) (which is about `optional` properties of protocols). I don't think we have a good workaround other than defining a little `static inline` function in Objective-C that will do the call for you without trying to check anything. ```objectivec NS_SWIFT_NAME(setDirectoryURL(_:for:)) static inline void setDirectoryURLForPanel(id panel, NSURL * _Nonnull url) { NSSavePanel *realPanel = (NSSavePanel *)panel; realPanel.directoryURL = url; } ``` An alternate approach in this specific case would be to file a bug against Apple that the `sender` here is not an instance of NSOpenPanel or at least NSSavePanel. ---
**Author:** ![pkamb](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/pkamb/32/2500_2.png) [@pkamb](https://forums.swift.org/u/pkamb)\ **Post date:** [October 3, 2018, 4:29am UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642/3 "2018-10-03T04:29:04Z")
Thank you for the quick reply. I'll try that workaround. I opened a JIRA bug here: Cannot assign to a property through AnyObject > > > | | | > |------------------|-----------------|… > |Previous ID | SR-8900 | > |Radar | rdar://problem/15233922 | > |Original Reporter | pkamb (JIRA User) | > |Type | Bug | > > \ > \Environment\ > > Swift 4.2, Xcode 10 > > > \ > > \ > \Additional Detail from JIRA\ > > | | | > |------------------|-----------------| > |Votes | 0 | > |Component/s | Compiler | > |Labels | Bug | > |Assignee | None | > |Priority | Medium | > > > > md5: fecd1beb40b55f31a3a7e32235cd1f19 > > \ > > > > > \*\*relates to\*\*: > \* \[SR-5475\](https://bugs.swift.org/browse/SR-5475) Can't set property declared optional in protocol > > > \*\*Issue Description:\*\* > > > Public bug for \\\ "Cannot assign to a property through AnyObject" > > I'm attempting to implement NSOpenSavePanelDelegate in a Sandboxed Mac app. > > The \\\`sender: Any\\\` parameter is a private system class that I cannot cast to. The private classes do not inherit from the public alternatives, so I cannot cast to those either. > > I'm forced to use AnyObject. But doing so results in the error \\\`Cannot assign to immutable expression\\\`. > > Sample Code: > > \`\`\` swift > extension PanelController: NSOpenSavePanelDelegate { > > func panel(\_ sender: Any, didChangeToDirectoryURL url: URL?) { > switch sender { > case is NSSavePanel: () // false > case is NSOpenPanel: () // false > default: > print("Sandboxed app. Uses private PowerBox open/save panel classes such as NSVBOpenPanel") > } > > var panel = sender as AnyObject > > // Error: Cannot assign to immutable expression of type 'URL?' > panel.directoryURL? = URL(fileURLWithPath: "/")! > } > > } > \`\`\` > > Also posted in the Swift Forums here: > \ ---
**Author:** ![eskimo](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/eskimo/32/13558_2.png) [@eskimo](https://forums.swift.org/u/eskimo)\ **Post date:** [October 3, 2018, 1:50pm UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642/4 "2018-10-03T13:50:22Z")
> Any suggestions for … getting a reference to the Panel? By way of workarounds, it seems like the `PanelController` class is intended to control a panel. In that case I’d store a reference to that panel in an instance property. That way my delegate could access it directly, rather than go through the `sender` parameter. Share and Enjoy Quinn “The Eskimo!” @ DTS @ Apple ---
**Author:** ![pkamb](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/pkamb/32/2500_2.png) [@pkamb](https://forums.swift.org/u/pkamb)\ **Post date:** [October 3, 2018, 6:09pm UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642/5 "2018-10-03T18:09:10Z")
Ok, that does work and is probably the best workaround: ``` if sender as AnyObject === myOpenPanel as AnyObject { myOpenPanel?.directoryURL = URL(fileURLWithPath: "/") } ``` Now I find that setting the directoryURL does not seem to work within the Sandbox! Ugh. I guess there is then no way to limit the OpenPanel to a single directory. ---
**Author:** ![eskimo](https://sea2.discourse-cdn.com/swift/user_avatar/forums.swift.org/eskimo/32/13558_2.png) [@eskimo](https://forums.swift.org/u/eskimo)\ **Post date:** [October 4, 2018, 4:10pm UTC](https://forums.swift.org/t/anyobject-parameter-cannot-assign-to-immutable-expression/16642/6 "2018-10-04T16:10:53Z")
> I guess there is then no way to limit the OpenPanel to a single > directory. Alas, I don’t know the answer to that one off the top of my head. You could ask over on [DevForums](https://forums.developer.apple.com/community/distribution/mac-app-sandbox) to see if anyone’s done that before. If that doesn’t work out, you should open a [DTS tech support incident](https://developer.apple.com/support/technical/) and speak to our App Sandbox expert. Share and Enjoy Quinn “The Eskimo!” @ DTS @ Apple