Re Ch.22 challenge: where to put @property (nonatomic) NSArr


The book says:
Move the property declaration for the array into a class extension in BNRPortfolio.m.

At first I took this to mean add the following to implementation file ( & remove the declaration for _thePortfolio from the header file):
@interface BNRPortfolio ()
NSMutableArray *_thePortfolio; // makes the portfolio mutable inside the class

This worked. However, the instructions says move the “property declaration.” Isn’t that this:
@property (nonatomic) NSArray *thePortfolio;

It didn’t work when I tried to move the above @property line of code from the header to the class extension in the implementation file.

Any thoughts?