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Note: The title of this page is a bit misleading. The actual topic has to do with a small part of introspection. Not class deallocation/destruction and dealloc method semantics.

The ObjC runtime stores a lot of information about a class - namely, all its methods, instance variables, and super-classes. This information is freely available to programmers, and is often more comprehensive than Apple’s documentation about its classes, for instance. Did you know that NSArray has a method called indexOf:::? I didn’t, nor do I know what it does…

Anyway, here’s the code that does it all:

#import </usr/include/objc/objc-class.h> #import </usr/include/objc/Protocol.h> #import <Foundation/Foundation.h>

void DeconstructClass(Class aClass) { struct objc_class *class = aClass; const char *name = class->name; int k; void *iterator = 0; struct objc_method_list *mlist;

NSLog(@"Deconstructing class %s, version %d",
      name, class->version);
NSLog(@"%s size: %d", name,
      class->instance_size);
if (class->ivars == nil)
    NSLog(@"%s has no instance variables", name);
else
    {
    NSLog(@"%s has %d ivar%c", name,
          class->ivars->ivar_count,
          ((class->ivars->ivar_count == 1)?' ':'s'));
    for (k = 0;
         k < class->ivars->ivar_count;
         k++)
        NSLog(@"%s ivar #%d: %s", name, k,
              class->ivars->ivar_list[k].ivar_name);
    }
mlist = class_nextMethodList(aClass, &iterator);
if (mlist == nil)
    NSLog(@"%s has no methods", name);
else do
    {
        for (k = 0; k < mlist->method_count; k++)
            {
            NSLog(@"%s implements %@", name,
                  NSStringFromSelector(mlist->method_list[k].method_name));
            }
    }
    while ( mlist = class_nextMethodList(aClass, &iterator) );

if (class->super_class == nil)
    NSLog(@"%s has no superclass", name);
else
    {
    NSLog(@"%s superclass: %s", name, class->super_class->name);
    DeconstructClass(class->super_class);
    } }

Here is a sample of its talents (on Mac OS X 10.1.3):

DeconstructClass([NSObject class]); produces:

Deconstructing class NSObject, version 0 NSObject size: 4 NSObject has 1 ivar NSObject ivar #0: isa NSObject implements _conformsToProtocolNamed: NSObject implements replacementObjectForPortCoder: NSObject implements classForPortCoder NSObject implements _cfTypeID NSObject implements methodFor: NSObject implements conformsTo: NSObject implements respondsTo: NSObject implements isKindOf: NSObject implements forward:: NSObject implements isNSIDispatchProxy NSObject implements replacementObjectForArchiver: NSObject implements classForArchiver NSObject implements performSelector:withObject:afterDelay:inModes: NSObject implements performSelector:object:afterDelay: NSObject implements performSelector:withObject:afterDelay: NSObject implements coerceValue:forKey: NSObject implements removeValueAtIndex:fromPropertyWithKey: NSObject implements insertValue:atIndex:inPropertyWithKey: NSObject implements replaceValueAtIndex:inPropertyWithKey:withValue: NSObject implements valueWithUniqueID:inPropertyWithKey: NSObject implements valueWithName:inPropertyWithKey: NSObject implements valueAtIndex:inPropertyWithKey: NSObject implements classCode NSObject implements className NSObject implements objectSpecifier NSObject implements isCaseInsensitiveLike: NSObject implements isLike: NSObject implements doesContain: NSObject implements isGreaterThan: NSObject implements isGreaterThanOrEqualTo: NSObject implements isLessThan: NSObject implements isLessThanOrEqualTo: NSObject implements isNotEqualTo: NSObject implements isEqualTo: NSObject implements removeObject:fromBothSidesOfRelationshipWithKey: NSObject implements addObject:toBothSidesOfRelationshipWithKey: NSObject implements _setObject:forBothSidesOfRelationshipWithKey: NSObject implements removeObject:fromPropertyWithKey: NSObject implements addObject:toPropertyWithKey: NSObject implements clearProperties NSObject implements allPropertyKeys NSObject implements isToManyKey: NSObject implements validateTakeValue:forKeyPath: NSObject implements validateValue:forKey: NSObject implements classDescriptionForDestinationKey: NSObject implements ownsDestinationObjectsForRelationshipKey: NSObject implements inverseForRelationshipKey: NSObject implements toManyRelationshipKeys NSObject implements toOneRelationshipKeys NSObject implements attributeKeys NSObject implements entityName NSObject implements classDescription NSObject implements createKeyValueBindingForKey:typeMask: NSObject implements _createKeyValueBindingForKey:name:bindingType: NSObject implements flushKeyBindings NSObject implements keyValueBindingForKey:typeMask: NSObject implements takeStoredValue:forKey: NSObject implements takeValue:forKey: NSObject implements storedValueForKey: NSObject implements valueForKey: NSObject implements unableToSetNilForKey: NSObject implements handleTakeValue:forUnboundKey: NSObject implements handleQueryWithUnboundKey: NSObject implements takeStoredValuesFromDictionary: NSObject implements takeValuesFromDictionary: NSObject implements valuesForKeys: NSObject implements takeValue:forKeyPath: NSObject implements valueForKeyPath: NSObject implements perform:withEachObjectInArray: NSObject implements implementsSelector: NSObject implements methodForSelector: NSObject implements doesNotRecognizeSelector: NSObject implements replacementObjectForCoder: NSObject implements classForCoder NSObject implements awakeAfterUsingCoder: NSObject implements performv:: NSObject implements forwardInvocation: NSObject implements methodSignatureForSelector: NSObject implements forward:: NSObject implements methodDescriptionForSelector: NSObject implements mutableCopy NSObject implements init NSObject implements dealloc NSObject implements copy NSObject implements zone NSObject implements superclass NSObject implements self NSObject implements retainCount NSObject implements retain NSObject implements respondsToSelector: NSObject implements release NSObject implements performSelector:withObject:withObject: NSObject implements performSelector:withObject: NSObject implements performSelector: NSObject implements isProxy NSObject implements isFault NSObject implements isMemberOfClass: NSObject implements isKindOfClass: NSObject implements isEqual: NSObject implements hash NSObject implements _copyDescription NSObject implements debugDescription NSObject implements description NSObject implements conformsToProtocol: NSObject implements class NSObject implements autorelease NSObject has no superclass

Anybody have any luck making this work in 10.3? It just SIGBUSs on me at class_nextMethodList.

OSX 10.3.4 with XCode 1.5 works like a charm.

Thats as very cool function! With a couple of trivial modifications it becomes a Category that you makes all objects able to deconstruct themselves:

** ClassDeconstruction.h **

#import <Cocoa/Cocoa.h>

@interface NSObject (ClassDeconstruction)

@end

** ClassDeconstruction.m **

#import “ClassDeconstruction.h” #import </usr/include/objc/objc-class.h> #import </usr/include/objc/Protocol.h> #import <Foundation/Foundation.h>

@implementation NSObject (ClassDeconstruction)

@end

Then use the category method like this: [self deconstruct];

I used the code below at some point. Not as clean as above, but can be useful too (there is more done with ivars, and some info about the method signatures). Sorry I am too lazy to make it a category right now (and I don’t want to break what works…). –CharlesParnot

TFUtilities.h

#import <Foundation/Foundation.h> @interface TFUtilities : NSObject {}

TFUtilities.m #import “TFUtilities.h” #import <objc/objc.h> #import <objc/objc-class.h> #import <objc/objc-runtime.h>

static NSString* TFMethodNameKey=@”method_name”; static NSString* TFMethodTypesKey=@”method_types”; static NSString* TFIvarNameKey=@”ivar_name”; static NSString* TFIvarTypeKey=@”ivar_type”; static NSString* TFIvarOffsetKey=@”ivar_offset”; static NSString* TFIvarObjectKey=@”ivar_object”;

@implementation TFUtilities

//returns an NSArray of NSDictionary //each item in the array = 1 ivar //dictionary = description of the ivar

//returns an [[NSArray of NSDictionary //each item in the array = 1 method //dictionary = description of the method