self
If you want to access a property of self using accessor methods, you must explicitly call out self as illustrated in this example:

self.age = 10;

If you do not use self., you access the instance variable directly. In the following example, the set
accessor method for the age property is not invoked:

age = 10;

p57, The Objective-C 2.0 Programming Language Language (v2008-06-09)
p22, The Objective-C 2.0 Programming Language Language (v2009-10-19)

So basically it’s a shortcut to:

int* a = [self age];
[self setAge:12];

(providing there is a setter/getter for age.)