Adopted by |
Various Cocoa classes |
Framework | /System/Library/Frameworks/Foundation.framework |
Availability | Available in Mac OS X v10.0 and later. |
Companion guide | |
Declared in | NSObject.h |
The NSCopying
protocol declares a method for providing functional copies of an object. 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, copyWithZone:
, but copying is commonly invoked with the convenience method copy
. The copy
method is defined for all objects inheriting from NSObject
and simply invokes copyWithZone:
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 copyWithZone:
.
Implement NSCopying
by invoking the superclass’s copyWithZone:
when NSCopying
behavior 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 copyWithZone:
to properly handle its own instance variables, invoking the superclass’s implementation first.
Returns a new instance that’s a copy of the receiver.
- (id)copyWithZone:(NSZone *)zone
The zone identifies an area of memory from which to allocate for the new instance. If zone is NULL
, the new instance is allocated from the default zone, which is returned from the function NSDefaultMallocZone
.
The returned object is implicitly retained by the sender, who is responsible for releasing it. The copy returned is immutable if the consideration “immutable vs. mutable” applies to the receiving object; otherwise the exact nature of the copy is determined by the class.
– mutableCopyWithZone:
(NSMutableCopying protocol)– copy
(NSObject class)NSObject.h
© 2006 Apple Computer, Inc. All Rights Reserved. (Last updated: 2006-05-23)