Allows you to add a "vulture": a block that will be executed when the object it's attached to is deallocated.

ArchVulture.h

#import <Foundation/Foundation.h>

@interface NSObject (addVulture)

// Do NOT use a block that captures this object.
// If you capture it strongly, you'll create a retain cycle.
// If you capture it weakly, you'll just get nil.
// If you capture it unsafely, you'll start calling methods on a mostly-dealloced object!

- (void)addVultureWithBlock:(dispatch_block_t)block;

@end

ArchVulture.m

#import "ArchVulture.h"
#import <objc/runtime.h>

@interface ArchVulture: NSObject

- (id)initWithBlock:(dispatch_block_t)block nextVulture:(ArchVulture*)nextVulture;

@property (copy) dispatch_block_t block;
@property (strong) ArchVulture * nextVulture;

@end

@implementation ArchVulture

- (id)initWithBlock:(dispatch_block_t)block nextVulture:(ArchVulture*)nextVulture {
    if((self = [super init])) {
		_block = [block copy];
		_nextVulture = nextVulture;
	}
	return self;
}

- (void)dealloc {
	_block();
}

@end

@implementation NSObject (addVulture)

- (void)addVultureWithBlock:(dispatch_block_t)block {
	// Make sure our ArchVulture objects aren't put in the parent autorelease pool, 
	// giving them a longer lifetime than intended.
	@autoreleasepool {
		ArchVulture * currentVulture = objc_getAssociatedObject(self, _cmd);
		ArchVulture * newVulture = [[ArchVulture alloc] initWithBlock:block nextVulture:currentVulture];
	
		objc_setAssociatedObject(self, _cmd, newVulture, OBJC_ASSOCIATION_RETAIN_NONATOMIC);
	}
}

@end

main.m

#import "ArchVulture.h"

int main(int argc, char *argv[]) {
	@autoreleasepool {
		NSObject * owner = [NSObject new];
		
		[owner addVultureWithBlock:^{
			NSLog(@"He's dead, Jim!");
		}];
		
		owner = nil;
	}
}