1@interface RootObject 2@end 3 4@interface BaseClass : RootObject 5@end 6 7@interface BaseClass() { 8 int _field1; 9} 10@property(atomic, assign, readonly) int field2; 11 12- (int)addFields; 13@end 14 15@implementation BaseClass 16- (int)addFields { 17 return self->_field1 + [self field2]; 18} 19@end 20 21