Are these two Objective-C message expressions equivalent memory-wise?

Do the following two message expressions result in an increase of retain count in the same object?

Example 1:

iVar = [Foo aClassMethodInFoo];
[iVar retain];

Example 2:

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iVar = [[Foo aClassMethodInFoo] retain];

Example 1 is explicit in that it's iVar instance whose retain count is increased. Example 2 seems to suggest that it's retain count of the object returned from [Foo aClassMethodInFoo] that is increased. If that is so, then assuming aClassMethodInFoo is a convenience method, which object do I 'release' to balance the earlier 'retain' in order not to leak memory?

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Both are absolutely identical. In the first case, you're assigning the results of a method call to a variable, then calling -retain on that variable. The net result is the variable holds the object, and you've called -retain on the object. In the second case, you're calling -retain on the results of a method call, and assigning the result of that to the variable. As -retain is guaranteed to return its receiver, the net result is the variable holds the object, and you've called -retain on the object.

In both cases, the memory semantics are precisely identical. According to the naming conventions defined in the Memory Management Programming Guide, a method named +aClassMethodInFoo returns an autoreleased object, so your call to -retain is correct if you're storing the results in an ivar. As such, when you're done you can call -release on your ivar. Your question of "which object do I 'release'" is nonsensical because there's only one object here.

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Assuming that the class method returns a new object rather than void, they are exactly equivalent because retain just returns self.