swift - Cast from AnyObject to UIEdgeInsets

Question

I'm trying to use KVO pattern on scrollView's contentInset and i need to know about old/new values. I know UIEdgeInests is a struct hence can not be stored in Dictionary, but i receive it in changes. this is my change Dictionary:

Optional(["old": UIEdgeInsets: {0, 0, 100, 0}, "new": UIEdgeInsets: {64, 0, 149, 0}, "kind": 1])

and this is how i'm trying to cast it:

guard let oldValue = change?[NSKeyValueChangeOldKey] as? UIEdgeInsets,
        newValue = change?[NSKeyValueChangeNewKey] as? UIEdgeInsets
        else { return }

But always fails.

Any ideas how to cast it into UIEdgeInsets?