NSCopying
A protocol that objects adopt to provide functional copies of themselves.
Declaration
protocol NSCopyingOverview
The exact meaning of “copy” can vary from class to class, but a copy must be a functionally independent object with values identical to the original at the time the copy was made. A copy produced with NSCopying is implicitly retained by the sender, who is responsible for releasing it.
NSCopying declares one method, copy(with:), but copying is commonly invoked with the convenience method copy(). The copy() method is defined for all objects inheriting from NSObject and simply invokes copy(with:) with the default zone.
Your options for implementing this protocol are as follows:
Implement NSCopying using alloc and
init...in classes that don’t inherit copy(with:).Implement NSCopying by invoking the superclass’s copy(with:) when
NSCopyingbehavior is inherited. If the superclass implementation might use the NSCopyObject function, make explicit assignments to pointer instance variables for retained objects.Implement NSCopying by retaining the original instead of creating a new copy when the class and its contents are immutable.
If a subclass inherits NSCopying from its superclass and declares additional instance variables, the subclass has to override copy(with:) to properly handle its own instance variables, invoking the superclass’s implementation first.