Associative Object は自動で release, property は自分で release ref: http://qiita.com/items/c262c9b9f8e1044ac2e4

file1.txt

$ clang main.m -o main -framework Cocoa && ./main
-[Container dealloc] 
-[Content dealloc] property
-[Content dealloc] associatedObject

main.m

/* clang main.m -o main -framework Cocoa && ./main */
#include <stdio.h>
#import <Cocoa/Cocoa.h>
#import <objc/runtime.h>

#define TRACE(msg) printf("%s %s\n", __PRETTY_FUNCTION__, msg)

@interface Content : NSObject
@property (nonatomic, retain) NSString *msg;
@end

@implementation Content

@synthesize msg=_msg;

- (id)initWithMessage:(NSString *)msg
{
    self = [super init];
    if (self) {
        self.msg = msg;
    }
    return self;
}

- (void)dealloc
{
    TRACE(self.msg.UTF8String);
    self.msg = nil;
    [super dealloc];
}
@end

@interface Container : NSObject
@property (nonatomic, retain) Content *content;
@end

static char associativeKey;
@implementation Container

@synthesize content=_content;

- (id)init
{
    self = [super init];
    if (self) {
        id associatedObject = [[[Content alloc] initWithMessage:@"associatedObject"] autorelease];
        objc_setAssociatedObject(self, &associativeKey, associatedObject, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
        self.content = [[[Content alloc] initWithMessage:@"property"] autorelease];
    }
    return self;
}

- (void)dealloc
{
    TRACE("");
    self.content = nil;
    [super dealloc];
}

@end

int main(int argc, char **argv)
{
    @autoreleasepool {
        [[Container new] autorelease];
    }
    return 0;
}