Question

What if I have an object, say NSIndexPath in which before I do a copy I always release it first?

Is it possible to have a memory count under 0?
I am doing this to prevent memory leaks.. is this a good way?

//global already has some value before in here or it doesn’t have a value.. I want to update
//this with a new value (I no longer care to the old pointer)

 [global release]
 global = [indexPath copy];

Answer 1

Don’t. When the retain count reaches 0, your object will be dealloc’ed and its pointer will become invalid, so using it again will cause unpredictable results (namely crashing).

You should read through Apple’s Memory Management Guide.

This is the fundamental rule:

• You only release or autorelease objects you own. You take ownership of an object if you create it using a method whose name begins with “alloc”, “new”, “copy”, or “mutableCopy” (for example, alloc, newObject, or mutableCopy), or if you send it a retain message.
• You use release or autorelease to relinquish ownership of an object. autorelease just means “send a release message in the future” (specifically: when the used autorelease pool receives a drain message).

Update:

As Josh pointed out, the one case you need to consider is when global and indexPath are the same. In that case, you would still “need” the pointer (to perform the copy), so you either autorelease (instead of releasing) or you use a temporary variable to handle that.