How does swift listen for extended properties?

public var dataList: Array<Any> {
        get {
            var list = objc_getAssociatedObject(self, AssociationKeyFromSelector(-sharpfunction)) as? Array<Any>;
            if list == nil {
                list = [];
                objc_setAssociatedObject(self, AssociationKeyFromSelector(-sharpfunction), list, .OBJC_ASSOCIATION_RETAIN_NONATOMIC);
            }
            return list!;
        }
        set {
            objc_setAssociatedObject(self, AssociationKeyFromSelector(-sharpfunction), newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        }
    }
Mar.13,2022
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