fix Any? cast to protocol always nil in ios 13

[wy-time]

It is a swift bug, In iOS 13 or earlier versions.
cast an Any? to protocol will always get nil
https://stackoverflow.com/questions/42033735/failing-cast-in-swift-from-any-to-protocol

In my case i use backgroundDecode option when download image, and if the image is a GIF the animate will lost, because the decode func not return itself

public func decoded(scale: CGFloat) -> KFCrossPlatformImage {
        // Prevent animated image (GIF) losing it's images
        #if os(iOS)
        if frameSource != nil { return base }
        #else
        if images != nil { return base }
        #endif
       ....... ........
    }

The frameSource always get nil, because the T in getAssociatedObject func is ImageFrameSource it is a protocol, so always return nil

func getAssociatedObject<T>(_ object: Any, _ key: UnsafeRawPointer) -> T? {
    return objc_getAssociatedObject(object, key) as? T // T is ImageFrameSource when get frameSource
}

The fix is first casting to AnyObject and then casting to the protocol
This swift bug was fixed in ios14 and macos 11 runtime

[onevcat]

@wy-time Thanks for reporting this. Umm, it is quite surprising.

I guess the similar issue might also happen on other platforms? Besides of only iOS and macOS, can you also try to add all of other supported platform versions to the check?

Maybe something like:

if #available(iOS 14.0, tvOS 14.0, macOS 11, watchOS 7.0, *) {
  //...

[wy-time]

ok,swift 5.3 fixed this issue, so I add if #available(iOS 14, macOS 11, watchOS 7, tvOS 14, *) check

[onevcat]

Great! Thanks for it.