NSMutableSet with weak references eg doesn't retain added objects

WeakReferenceSet.m

//  WeakReferenceSet.h
//  Created by chris.hulbert@gmail.com on 21/06/11.

#import <Foundation/Foundation.h>

@interface WeakReferenceSet : NSObject

+ (WeakReferenceSet*)set;
- (void)addObject:(id)object;
- (void)removeObject:(id)object;
- (void)removeAllObjects;
- (NSArray *)allObjects;

@end

//  WeakReferenceSet.m
//  Created by Chris (chris.hulbert@gmail.com) on 21/06/11.

#import "WeakReferenceSet.h"

// Declaration of private properties
@interface WeakReferenceSet()
@property (nonatomic,retain) NSMutableSet *internalSet;
@end

@implementation WeakReferenceSet
@synthesize internalSet=_internalSet;

// Dealloc, freeing everything from the list without affecting their retain count
-(void)dealloc {
    [self removeAllObjects]; // So that the normal nsmutableset's dealloc doesn't release them all
    self.internalSet = nil;
    [super dealloc];
}

// Constructor
-(id)init {
    self = [super init];
    if (self) {
        self.internalSet = [NSMutableSet set];
    }
    return self;
}

// Creates an autoreleased weak reference set
+(WeakReferenceSet *)set {
    return [[[self alloc] init] autorelease];
}

// Remove everything
- (void)removeAllObjects {
    while (self.internalSet.count) {
        [self removeObject:self.internalSet.anyObject];
    }
}

// Adds an object to the set, however does not allow the reference count to be incremented, as we wish to have a weak reference
-(void)addObject:(id)object {
    if (![self.internalSet containsObject:object]) {
        [self.internalSet addObject:object]; // This will do a retain
        [object release]; // So here, we release it to counter the retain
    }
}

// Removes an object from the set, countering the normal release that this triggers
-(void)removeObject:(id)object {
    if ([self.internalSet containsObject:object]) {
        [object retain]; // Do a retain, to counter the release that follows
        [self.internalSet removeObject:object]; // This does a release
    }
}

// Access the list of objects so that you can iterate through it and eg send your observers a message
-(NSArray *)allObjects {
    return self.internalSet.allObjects;
}

@end