How to cast NSString to AnyObject?

[crutchcorn]

Apologies for this being a naive question, I'm new to Rust and even newer to objc2.

Looking at Apple's docs for MPNowPlayingInfoCenter's nowPlayingInfo, I see:

var nowPlayingInfo: [String : Any]? { get set }

But this Any is the cause of some headaches for me. According to the reference docs, the following should be allowed:

  func setNowPlayingMetadata(_ metadata: NowPlayableStaticMetadata) {
       
        let nowPlayingInfoCenter = MPNowPlayingInfoCenter.default()
        var nowPlayingInfo = [String: Any]()
        
        NSLog("%@", "**** Set track metadata: title \(metadata.title)")
        nowPlayingInfo[MPNowPlayingInfoPropertyAssetURL] = metadata.assetURL
        nowPlayingInfo[MPNowPlayingInfoPropertyMediaType] = metadata.mediaType.rawValue
        nowPlayingInfo[MPNowPlayingInfoPropertyIsLiveStream] = metadata.isLiveStream
        nowPlayingInfo[MPMediaItemPropertyTitle] = metadata.title
        nowPlayingInfo[MPMediaItemPropertyArtist] = metadata.artist
        nowPlayingInfo[MPMediaItemPropertyArtwork] = metadata.artwork
        nowPlayingInfo[MPMediaItemPropertyAlbumArtist] = metadata.albumArtist
        nowPlayingInfo[MPMediaItemPropertyAlbumTitle] = metadata.albumTitle
        
        nowPlayingInfoCenter.nowPlayingInfo = nowPlayingInfo
    }

However, when trying to do the same with Rust:

pub fn set_now_playing() {
    unsafe {
        let default = MPNowPlayingInfoCenter::defaultCenter();
        MPNowPlayingInfoCenter::setNowPlayingInfo(&*default, {
            let keys = &[
                MPNowPlayingInfoPropertyAssetURL,
                MPNowPlayingInfoPropertyMediaType,
                MPNowPlayingInfoPropertyIsLiveStream,
                MPMediaItemPropertyTitle,
                MPMediaItemPropertyArtist,
                MPMediaItemPropertyArtwork,
                MPMediaItemPropertyAlbumArtist,
                MPMediaItemPropertyAlbumTitle
            ];
            let owned_objects = &[
                NSString::from_str("https://example.com"),
                NSString::from_str("1"),
                NSString::from_str("false"),
                NSString::from_str("Title"),
                NSString::from_str("Artist"),
                NSString::from_str("Artwork"),
                NSString::from_str("Album Artist"),
                NSString::from_str("Album Title")
            ];
            Some(objc2_foundation::NSDictionary::from_id_slice(keys, owned_objects).as_ref())
        });
    }
}

I get an error:

mismatched types
expected reference `&NSDictionary<_, AnyObject>`
   found reference `&NSDictionary<_, NSString>`rustcClick for full compiler diagnostic

How can I fix this?

[madsmtm]

There are several ways around it, and unfortunately none of them very pretty :/.

One of them is something like:

let owned_objects: &[Retained<AnyObject>] = &[
    Retained::into_super(Retained::into_super(NSString::from_str("https://example.com"))),
    Retained::into_super(Retained::into_super(NSString::from_str("1"))),
    Retained::into_super(Retained::into_super(NSString::from_str("false"))),
    Retained::into_super(Retained::into_super(NSString::from_str("Title"))),
    Retained::into_super(Retained::into_super(NSString::from_str("Artist"))),
    Retained::into_super(Retained::into_super(NSString::from_str("Artwork"))),
    Retained::into_super(Retained::into_super(NSString::from_str("Album Artist"))),
    Retained::into_super(Retained::into_super(NSString::from_str("Album Title")),
];

And in the soon-to-be-released objc2-foundation v0.3, it'll look like this:

let owned_objects: &[Retained<AnyObject>] = &[
    NSString::from_str("https://example.com").into(),
    NSString::from_str("1").into(),
    NSString::from_str("false").into(),
    NSString::from_str("Title").into(),
    NSString::from_str("Artist").into(),
    NSString::from_str("Artwork").into(),
    NSString::from_str("Album Artist").into(),
    NSString::from_str("Album Title").into(),
];

Which is better, but still not great. Doing the kind of upcasting you desire (NSDictionary<X, Y> -> NSDictionary<X, AnyObject>) is tracked in #654.