NSSecureCoding

Historically, many classes decoded instances of themselves like this:

if let object = decoder.decodeObject(forKey: "myKey") as? MyClass {
    ...succeeds...
} else {
    ...fail...
}

This technique is potentially unsafe because by the time you can verify the class type, the object has already been constructed, and if this is part of a collection class, potentially inserted into an object graph.

In order to conform to NSSecureCoding:

• An object that does not override init(coder:) can conform to NSSecureCoding without any changes (assuming that it is a subclass of another class that conforms).

• An object that does override init(coder:) must decode any enclosed objects using the decodeObject(of:forKey:) method. For example:

  let obj = decoder.decodeObject(of: MyClass.self, forKey: "myKey")

  In addition, the class must override its NSSecureCoding method to return true.