Question

I was wondering what exactly are the differences between using the (get) accessor for reading the value of property and directly using the iVar?

Say I have a class which declares a property:

@interface Foo : NSObject

@property (strong) NSString *someString;

@end

And in the implementation I’m using it. Are there any differences between the following two lines:

someLabel.text = self.someString;

someLabel.text = _someString;

For set accessors it’s clear. Afaik for strong properties the accessor takes care of retain and release (an interesting ‘side question’ would be if ARC changes that, i.e. does setting the iVar directly [assuming it’s not an __weak iVar] also retain and release correctly using ARC), also KVO requires the use of accessors to work properly etc. But what about getters?

And if there’s no difference, is there one way considered best practice?

Thx

Answer 1

As you know, calling self.someString is really [self someString]. If you chose to create a property then you should use the property. There may be other semantics added to the property. Perhaps the property is lazy loaded. Perhaps the property doesn’t use an ivar. Perhaps there is some other needed side effect to calling the property’s getter. Maybe there isn’t now but maybe this changes in the future. Calling the property now makes your code a little more future proof.

If you have an ivar and a property, use the property unless you have explicit reason to use the ivar instead. There may be a case where you don’t want any of the extra semantics or side effect of the property to be performed. So in such a case, using the ivar directly is better.

But ultimately, it’s your code, your property, your ivar. You know why you added a property. You know any potential benefits of that property, if any.