Swift-Extension
add property in extension
generally extension can’t add peoperty
class extensionClass {
}extension extensionClass {
private static var propertyKey: UInt8 = 0var property: People? {set {objc_setAssociatedObject(self, &Self.propertyKey, newValue, .OBJC_ASSOCIATION_RETAIN_NONATOMIC)}get {objc_getAssociatedObject(self,&Self.propertyKey) as? People}}
}