The compiler only automatically synthesizes the instance variable for a property if it has to synthesize at least one accessor method.
If you implement both setter and getter method for your property (or if you implement the getter for a read-only property), the instance variable is not synthesized automatically.
In this case you have to add
@synthesize myArray = _myArray;
explicitly if you need the instance variable. Alternatively, you can declare
_myArray
as an ivar in the class extension.