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<title>NSObject</title>
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<dt><a href ="http://www.gnustep.org/developers/whoiswho.html">Richard Frith-Macdonald</a>
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<dt><a href ="http://www.gnustep.org/developers/whoiswho.html">Nicola Pero</a>
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<p>Version: $Revision: 1.16 $</p>
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<p>Date: $Date: 2001/12/12 14:10:13 $</p>
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<h2><a name ="cont-0">NSObject</a></h2>
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<h2><a name ="NSObject">NSObject</a></h2>
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<p><b>Declared in: </b> Foundation/NSObject.h</p>
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<p><b>Conforms to: </b> NSObject
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<code>NSObject</code> is the root class (a root class is
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a class with no superclass) of the gnustep base library
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class hierarchy, so all classes normally inherit from
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<code>NSObject</code>. There is an exception though:
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<code>NSProxy</code> (which is used for remote messaging)
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does not inherit from <code>NSObject</code>.
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Unless you are really sure of what you are doing, all
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your own classes should inherit (directly or indirectly)
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from <code>NSObject</code> (or in special cases from
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<code>NSProxy</code>). <code>NSObject</code> provides
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the basic common functionality shared by all gnustep
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The essential methods which must be implemented by all
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classes for their instances to be usable within gnustep
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are declared in a separate protocol, which is the
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<code>NSObject</code> protocol. Both
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<code>NSObject</code> and <code>NSProxy</code> conform to
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this protocol, which means all objects in a gnustep
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application will conform to this protocol (btw, if you
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don't find a method of <code>NSObject</code> you are
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looking for in this documentation, make sure you also
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look into the documentation for the <code>NSObject</code>
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Theoretically, in special cases you might need to
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implement a new root class. If you do, you need to make
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sure that your root class conforms (at least) to the
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<code>NSObject</code> protocol, otherwise it will not
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interact correctly with the gnustep framework. Said
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that, I must note that I have never seen a case in which
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a new root class is needed.
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<code>NSObject</code> is a root class, which implies that
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instance methods of <code>NSObject</code> are treated in
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a special way by the Objective-C runtime. This is an
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exception to the normal way messaging works with class
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and instance methods: if the Objective-C runtime can't
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find a class method for a class object, as a last resort
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it looks for an instance method of the root class with
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the same name, and executes it if it finds it. This
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means that instance methods of the root class (such as
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<code>NSObject</code>) can be performed by class objects
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which inherit from that root class ! This can only
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happen if the class doesn't have a class method with the
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same name, otherwise that method - of course - takes the
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precedence. Because of this exception,
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<code>NSObject</code>'s instance methods are written in
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such a way that they work both on <code>NSObject</code>'s
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instances and on class objects.
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<h2>Instance Variables </h2>
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<li ><a href ="NSObject.html#method-0">+alloc</a>
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<li ><a href ="NSObject.html#method-1">+allocWithZone:</a>
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<li ><a href ="NSObject.html#method-2">+cancelPreviousPerformRequestsWithTarget:selector:</a>
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<li ><a href ="NSObject.html#method-3">+class</a>
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<li ><a href ="NSObject.html#method-4">+conformsToProtocol:</a>
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<li ><a href ="NSObject.html#method-5">+copyWithZone:</a>
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<li ><a href ="NSObject.html#method-6">+description</a>
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<li ><a href ="NSObject.html#method-7">+descriptionWithLocale:</a>
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<li ><a href ="NSObject.html#method-8">+descriptionWithLocale:indent:</a>
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<li ><a href ="NSObject.html#method-9">+descriptionWithLocale:indent:to:</a>
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<li ><a href ="NSObject.html#method-10">+initialize</a>
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<li ><a href ="NSObject.html#method-11">+instanceMethodForSelector:</a>
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<li ><a href ="NSObject.html#method-12">+instanceMethodSignatureForSelector:</a>
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<li ><a href ="NSObject.html#method-13">+instancesRespondToSelector:</a>
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<li ><a href ="NSObject.html#method-14">+load</a>
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<li ><a href ="NSObject.html#method-15">+mutableCopyWithZone:</a>
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<li ><a href ="NSObject.html#method-16">+new</a>
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<li ><a href ="NSObject.html#method-17">+poseAsClass:</a>
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<li ><a href ="NSObject.html#method-18">+setVersion:</a>
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<li ><a href ="NSObject.html#method-19">+superclass</a>
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<li ><a href ="NSObject.html#method-20">+version</a>
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<li ><a href ="NSObject.html#method-47">-_dealloc</a>
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<li ><a href ="NSObject.html#method-21">-awakeAfterUsingCoder:</a>
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<li ><a href ="NSObject.html#method-22">-classForArchiver</a>
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<li ><a href ="NSObject.html#method-23">-classForCoder</a>
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<li ><a href ="NSObject.html#method-24">-classForPortCoder</a>
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<li ><a href ="NSObject.html#method-25">-connection:handleRequest:</a>
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<li ><a href ="NSObject.html#method-26">-copy</a>
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<li ><a href ="NSObject.html#method-27">-dealloc</a>
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<li ><a href ="NSObject.html#method-45">-deallocNotificationsActive</a>
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<li ><a href ="NSObject.html#method-28">-description</a>
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<li ><a href ="NSObject.html#method-29">-descriptionWithLocale:</a>
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<li ><a href ="NSObject.html#method-30">-descriptionWithLocale:indent:</a>
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<li ><a href ="NSObject.html#method-31">-descriptionWithLocale:indent:to:</a>
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<li ><a href ="NSObject.html#method-32">-doesNotRecognizeSelector:</a>
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<li ><a href ="NSObject.html#method-33">-forwardInvocation:</a>
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<li ><a href ="NSObject.html#method-34">-hash</a>
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<li ><a href ="NSObject.html#method-35">-init</a>
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<li ><a href ="NSObject.html#method-36">-isEqual:</a>
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<li ><a href ="NSObject.html#method-37">-methodForSelector:</a>
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<li ><a href ="NSObject.html#method-38">-methodSignatureForSelector:</a>
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<li ><a href ="NSObject.html#method-39">-mutableCopy</a>
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<li ><a href ="NSObject.html#method-40">-performSelector:withObject:</a>
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<li ><a href ="NSObject.html#method-41">-performSelector:withObject:afterDelay:inModes:</a>
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<li ><a href ="NSObject.html#method-42">-replacementObjectForArchiver:</a>
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<li ><a href ="NSObject.html#method-43">-replacementObjectForCoder:</a>
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<li ><a href ="NSObject.html#method-44">-replacementObjectForPortCoder:</a>
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<li ><a href ="NSObject.html#method-46">-setDeallocNotificationsActive:</a>
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<hr><h2>Class Methods </h2>
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<h3><a name ="method-0">alloc</a></h3>
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+ (id) <b>alloc</b>;<br>
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Allocates a new instance of the receiver from the default
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zone, by invoking <code>allocWithZone:</code> with
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<code>NSDefaultMallocZone()</code> as the zone argument.
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Returns the created instance.
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<h3><a name ="method-1">allocWithZone:</a></h3>
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+ (id) <b>allocWithZone:</b> (NSZone*)zone;<br>
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This is the basic method to create a new instance. It
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allocates a new instance of the receiver from the specified
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Memory for an instance of the receiver is allocated; a
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pointer to this newly created instance is returned. All
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instance variables are set to 0 except the
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<code>isa</code> pointer which is set to point to the
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object class. No initialization of the instance is
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performed: it is your responsibility to initialize the
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instance by calling an appropriate <code>init</code>
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method. If you are not using the garbage collector, it is
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also your responsibility to make sure the returned
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instance is destroyed when you finish using it, by calling
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the <code>release</code> method to destroy the instance
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directly, or by using <code>autorelease</code> and
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You do not normally need to override this method in
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subclasses, unless you are implementing a class which for
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some reasons silently allocates instances of another class
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(this is typically needed to implement class clusters and
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similar design schemes).
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If you have turned on debugging of object allocation (by
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calling the <code>GSDebugAllocationActive</code>
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function), this method will also update the various
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debugging counts and monitors of allocated objects, which
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you can access using the <code>GSDebugAllocation...</code>
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<h3><a name ="method-2">cancelPreviousPerformRequestsWithTarget:selector:</a></h3>
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+ (void) <b>cancelPreviousPerformRequestsWithTarget:</b> (id)aTarget <b>selector:</b> (SEL)aSelector;<br>
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<h3><a name ="method-3">class</a></h3>
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+ (Class) <b>class</b>;<br>
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Returns the receiver.
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<h3><a name ="method-4">conformsToProtocol:</a></h3>
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+ (BOOL) <b>conformsToProtocol:</b> (Protocol*)aProtocol;<br>
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<h3><a name ="method-5">copyWithZone:</a></h3>
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+ (id) <b>copyWithZone:</b> (NSZone*)zone;<br>
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<h3><a name ="method-6">description</a></h3>
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+ (NSString*) <b>description</b>;<br>
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The <code>description</code> factory method describes the class
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of the receiver. In the default GNUstep implementation, this
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simply returns the name of the class as an NSString object.
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<h3><a name ="method-7">descriptionWithLocale:</a></h3>
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+ (NSString*) <b>descriptionWithLocale:</b> (NSDictionary*)aLocale;<br>
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Standards: GNUstep<br>
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The default (NSOBject) implementation of this method simply calls
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the <code>description</code> method and discards the locale
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<h3><a name ="method-8">descriptionWithLocale:indent:</a></h3>
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+ (NSString*) <b>descriptionWithLocale:</b> (NSDictionary*)aLocale <b>indent:</b> (unsigned int)level;<br>
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Standards: GNUstep<br>
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The default (NSObject) implementation of this method simply calls
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the <code>descriptionWithLocale:</code> method and discards the
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<h3><a name ="method-9">descriptionWithLocale:indent:to:</a></h3>
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+ (NSString*) <b>descriptionWithLocale:</b> (NSDictionary*)aLocale <b>indent:</b> (unsigned int)level <b>to:</b> (id<GNUDescriptionDestination>)output;<br>
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Standards: GNUstep<br>
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The default (NSObject) implementation of this method simply calls
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the <code>descriptionWithLocale:indent:</code> method and appends
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the value returned by that method to the output object.
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<h3><a name ="method-10">initialize</a></h3>
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+ (void) <b>initialize</b>;<br>
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<h3><a name ="method-11">instanceMethodForSelector:</a></h3>
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+ (IMP) <b>instanceMethodForSelector:</b> (SEL)aSelector;<br>
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<h3><a name ="method-12">instanceMethodSignatureForSelector:</a></h3>
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+ (NSMethodSignature*) <b>instanceMethodSignatureForSelector:</b> (SEL)aSelector;<br>
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Returns a method signature object representing the
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method implemented for instsances of this class which
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corresponds to the supplied selector.
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<h3><a name ="method-13">instancesRespondToSelector:</a></h3>
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+ (BOOL) <b>instancesRespondToSelector:</b> (SEL)aSelector;<br>
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<h3><a name ="method-14">load</a></h3>
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+ (void) <b>load</b>;<br>
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<h3><a name ="method-15">mutableCopyWithZone:</a></h3>
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+ (id) <b>mutableCopyWithZone:</b> (NSZone*)zone;<br>
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<h3><a name ="method-16">new</a></h3>
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+ (id) <b>new</b>;<br>
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This method is a short-hand for alloc followed by init, that is,
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NSObject *object = [NSObject new];
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is exactly the same as
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NSObject *object = [[NSObject alloc] init];
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This is a general convention: all <code>new...</code>
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methods are supposed to return a newly allocated and
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initialized instance, as would be generated by an
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<code>alloc</code> method followed by a corresponding
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<code>init...</code> method. Please note that if you are
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not using a garbage collector, this means that instances
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generated by the <code>new...</code> methods are not
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autoreleased, that is, you are responsible for releasing
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(autoreleasing) the instances yourself. So when you use
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<code>new</code> you typically do something like:
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NSMutableArray *array = AUTORELEASE ([NSMutableArray new]);
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You do no normally need to override <code>new</code> in
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subclasses, because if you override <code>init</code> (and
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optionally <code>allocWithZone:</code> if you really
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need), <code>new</code> will automatically use your
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You might need instead to define new <code>new...</code>
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methods specific to your subclass to match any
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<code>init...</code> specific to your subclass. For
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example, if your subclass defines
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<code>-initWithName:</code>
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it might be handy for you to have a
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<code>+newWithName:</code>
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which combines <code>alloc</code> and
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<code>initWithName:</code>. You would implement it as follows:
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+ (id) newWithName: (NSString *)aName
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return [[self alloc] initWithName: aName];
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<h3><a name ="method-17">poseAsClass:</a></h3>
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+ (void) <b>poseAsClass:</b> (Class)aClass;<br>
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<h3><a name ="method-18">setVersion:</a></h3>
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+ (void) <b>setVersion:</b> (int)aVersion;<br>
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<h3><a name ="method-19">superclass</a></h3>
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+ (Class) <b>superclass</b>;<br>
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<h3><a name ="method-20">version</a></h3>
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+ (int) <b>version</b>;<br>
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<hr><h2>Instances Methods </h2>
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<h3><a name ="method-21">awakeAfterUsingCoder:</a></h3>
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- (id) <b>awakeAfterUsingCoder:</b> (NSCoder*)aDecoder;<br>
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<h3><a name ="method-22">classForArchiver</a></h3>
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- (Class) <b>classForArchiver</b>;<br>
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<h3><a name ="method-23">classForCoder</a></h3>
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- (Class) <b>classForCoder</b>;<br>
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<h3><a name ="method-24">classForPortCoder</a></h3>
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- (Class) <b>classForPortCoder</b>;<br>
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<h3><a name ="method-25">connection:handleRequest:</a></h3>
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- (BOOL) <b>connection:</b> (NSConnection*)connection <b>handleRequest:</b> (NSDistantObjectRequest*)doreq;<br>
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<h3><a name ="method-26">copy</a></h3>
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- (id) <b>copy</b>;<br>
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<h3><a name ="method-27">dealloc</a></h3>
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- (void) <b>dealloc</b>;<br>
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<code>NSObject</code>'s implementation of this method
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destroys the receiver, by returning the memory allocated
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to the receiver to the system. After this method has been
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called on an instance, you must not refer the instance in
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any way, because it does not exist any longer. If you do,
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it is a bug and your program might even crash with a
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If you have turned on the debugging facilities for
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instance allocation, <code>NSObject</code>'s
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implementation of this method will also update the various
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counts and monitors of allocated instances (see the
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<code>GSDebugAllocation...</code> functions for more
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Normally you are supposed to manage the memory taken by
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objects by using the high level interface provided by the
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<code>retain</code>, <code>release</code> and
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<code>autorelease</code> methods (or better by the
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corresponding macros <code>RETAIN</code>,
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<code>RELEASE</code> and <code>AUTORELEASE</code>), and by
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autorelease pools and such; whenever the
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release/autorelease mechanism determines that an object is
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no longer needed (which happens when its retain count
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reaches 0), it will call the <code>dealloc</code> method
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to actually deallocate the object. This means that normally,
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you should not need to call <code>dealloc</code> directly as
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the gnustep base library automatically calls it for you when
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the retain count of an object reaches 0.
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Because the <code>dealloc</code> method will be called
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when an instance is being destroyed, if instances of your
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subclass use objects or resources (as it happens for most
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useful classes), you must override <code>dealloc</code> in
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subclasses to release all objects and resources which are
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used by the instance, otherwise these objects and
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resources would be leaked. In the subclass
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implementation, you should first release all your subclass
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specific objects and resources, and then invoke super's
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implementation (which will do the same, and so on up in
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the class hierarchy to <code>NSObject</code>'s
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implementation, which finally destroys the object). Here
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is an example of the implementation of
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<code>dealloc</code> for a subclass whose instances have a
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single instance variable <code>name</code> which needs to
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be released when an instance is deallocated:
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<code>dealloc</code> might contain code to release not
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only objects, but also other resources, such as open
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files, network connections, raw memory allocated in other
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<h3><a name ="method-28">description</a></h3>
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- (NSString*) <b>description</b>;<br>
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The <code>description</code> method describes the reciever.
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In the default GNUstep implementation, this returns an NSString
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object giving the name of the class of the receiver and the
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hexadecimal representation of the recievers address enclosed
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Generally, classes other than NSObject will override this method
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to provide a more informative description of their instances.
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<h3><a name ="method-29">descriptionWithLocale:</a></h3>
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- (NSString*) <b>descriptionWithLocale:</b> (NSDictionary*)aLocale;<br>
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Standards: GNUstep<br>
534
The default (NSOBject) implementation of this method simply calls
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the <code>description</code> method and discards the locale
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<h3><a name ="method-30">descriptionWithLocale:indent:</a></h3>
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- (NSString*) <b>descriptionWithLocale:</b> (NSDictionary*)aLocale <b>indent:</b> (unsigned int)level;<br>
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Standards: GNUstep<br>
543
The default (NSObject) implementation of this method simply calls
544
the <code>descriptionWithLocale:</code> method and discards the
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<h3><a name ="method-31">descriptionWithLocale:indent:to:</a></h3>
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- (NSString*) <b>descriptionWithLocale:</b> (NSDictionary*)aLocale <b>indent:</b> (unsigned int)level <b>to:</b> (id<GNUDescriptionDestination>)output;<br>
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Standards: GNUstep<br>
552
The default (NSObject) implementation of this method simply calls
553
the <code>descriptionWithLocale:indent:</code> method and appends
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the value returned by that method to the output object.
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Property-list classes (NSString, NSArray, NSDictionary and
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NSData) will override this method in order to efficiently
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write descriptions of themselves into property lists.
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<h3><a name ="method-32">doesNotRecognizeSelector:</a></h3>
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- (void) <b>doesNotRecognizeSelector:</b> (SEL)aSelector;<br>
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<h3><a name ="method-33">forwardInvocation:</a></h3>
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- (void) <b>forwardInvocation:</b> (NSInvocation*)anInvocation;<br>
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<h3><a name ="method-34">hash</a></h3>
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- (unsigned int) <b>hash</b>;<br>
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<h3><a name ="method-35">init</a></h3>
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- (id) <b>init</b>;<br>
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<h3><a name ="method-36">isEqual:</a></h3>
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- (BOOL) <b>isEqual:</b> (id)anObject;<br>
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<h3><a name ="method-37">methodForSelector:</a></h3>
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- (IMP) <b>methodForSelector:</b> (SEL)aSelector;<br>
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<h3><a name ="method-38">methodSignatureForSelector:</a></h3>
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- (NSMethodSignature*) <b>methodSignatureForSelector:</b> (SEL)aSelector;<br>
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Returns a method signature object representing the
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method implemented in this object which corresponds to
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the supplied selector.
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<h3><a name ="method-39">mutableCopy</a></h3>
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- (id) <b>mutableCopy</b>;<br>
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<h3><a name ="method-40">performSelector:withObject:</a></h3>
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- (void) <b>performSelector:</b> (SEL)aSelector <b>withObject:</b> (id)anArgument;<br>
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<h3><a name ="method-41">performSelector:withObject:afterDelay:inModes:</a></h3>
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- (void) <b>performSelector:</b> (SEL)aSelector <b>withObject:</b> (id)anArgument <b>afterDelay:</b> (NSTimeInterval)delay <b>inModes:</b> (NSArray*)modes;<br>
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<h3><a name ="method-42">replacementObjectForArchiver:</a></h3>
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- (id) <b>replacementObjectForArchiver:</b> (NSArchiver*)anArchiver;<br>
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<h3><a name ="method-43">replacementObjectForCoder:</a></h3>
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- (id) <b>replacementObjectForCoder:</b> (NSCoder*)aCoder;<br>
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<h3><a name ="method-44">replacementObjectForPortCoder:</a></h3>
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- (id) <b>replacementObjectForPortCoder:</b> (NSPortCoder*)aCoder;<br>
632
<h3><a name ="method-45">deallocNotificationsActive</a></h3>
633
- (BOOL) <b>deallocNotificationsActive</b>;<br>
637
Returns a boolean indicating whether deallocation notification
643
If deallocation notification is turned on, whenever an objects
644
retain count reaches zero (and it would normally be deallocated)
645
the <em>_dealloc</em> methiod is called and the object is only
646
deallocated if that method returns YES.
651
<h3><a name ="method-46">setDeallocNotificationsActive:</a></h3>
652
- (void) <b>setDeallocNotificationsActive:</b> (BOOL)flag;<br>
656
Turns on (or off) deallocation notification.
661
If deallocation notification is turned on, whenever an objects
662
retain count reaches zero (and it would normally be deallocated)
663
the <em>_dealloc</em> methiod is called and the object is only
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deallocated if that method returns YES.
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<h3><a name ="method-47">_dealloc</a></h3>
670
- (BOOL) <b>_dealloc</b>;<br>
674
Returns a boolean indicating whether the receiver should be
675
deallocated or not. The default implementation returns YES.
680
This method is called when an objects retain count reaches
681
zero (if deallocation notifications are active).
686
This method is provided so that you can take some sort of
687
action when objects are deallocated ... normally you would
688
override this method in your classes, but you could also
689
override it in a category of NSObject - and perform some
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action whenever <em>any</em> object is deallocated.
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