Everyone stay calm, these zombies don’t mean any harm!

In Cocoa, objects released from memory will be kept around as “Zombies” if you enable a flag named NSZombieEnabled.

An attempt to access a freed object is a common bug in Cocoa Programming that leads to a crash. NSZombieEnabled helps you save a lot of time debugging your message to Zombie (released object).

When you try to call a de-allocated object with the NSZombieEnabled flag set, you will be notified by recording stops rather than simply crashing your application.

To enable this power move:

• Select “Edit Scheme…” from the “Product” menu (or, press Cmd+Shift+<).
• Select the “Run” on the left side of the scheme editor.
• Select the “Arguments” tab in right side page.
• Add a new item (press ‘+’) in Environment Variable and call it NSZombieEnabled.
• Set its value to YES.

Any more calls to the zombie after this will ask the system to stop the program by running a breakpoint, and you can take a look at the chain of calls that the zombie sends in the backtrack.

Learn more about it here.