override property from superclass in subclass

Question

I want to override an NSString property declared in a superclass. When I try to do it using the default ivar, which uses the the same name as the property but with an unders

Answer 1

to access the superclass variables, they must be marked as @protected, access to such variables will be only inside the class and its heirs

@interface ObjectA : NSObject
{
    @protected NSObject *_myProperty;
}
@property (nonatomic, strong, readonly) NSObject *myProperty;
@end

@interface ObjectB : ObjectA
@end

@implementation ObjectA
@synthesize myProperty = _myProperty;
@end

@implementation ObjectB
- (id)init
{
    self = [super init];
    if (self){
        _myProperty = [NSObject new];
    }
    return self;
}
@end

Answer 2

Only the superclass has access to the ivar _species. Your subclass should look like this:

- (NSString *)species {
    NSString *value = [super species];
    if (!value) {
        self.species = @"Homo sapiens";
    }

    return [super species];
}

That sets the value to a default if it isn't currently set at all. Another option would be:

- (NSString *)species {
    NSString *result = [super species];
    if (!result) {
        result = @"Home sapiens";
    }

    return result;
}

This doesn't update the value if there is no value. It simply returns a default as needed.