Class - Person @interface Person : NSObject @property (nonatomic, copy) NSString *lastName; @end @implementation Person @synthesize lastName = _lastName; - (instancetype)init { self = [super init]; if (self) { _lastName = @"abc"; } return self; } - (NSString *)lastName { return _lastName; } - (void)setLastName:(NSString *)lastName { _lastName = lastName; } @end Class - SmithPerson @interface SmithPerson : Person @end @implementation SmithPerson - (instancetype)init { self = [super init]; if (self) { self.lastName = @"aaa"; } return self; } @end

以上在子类SmithPerson中没有重写lastName的getter/setter方法，我可以在init中通过self.lastName重新赋值，但是如果我在子类重写了getter/setter，那怎么重新赋值呢？self.lastName会调用子类的setter方法，setter中如果这样赋值就死循环了

- (void)setLastName:(NSString *)lastName { self.lastName = lastName; }

另外：如果将Person和SmithPerson的init方法改成下面这样，同时子类重写父类lastName的getter/setter：

Person - (instancetype)init { self = [super init]; if (self) { **self.lastName = @"abc";** } return self; } SmithPerson - (instancetype)init { self = [super init]; if (self) { } return self; }

那么执行下面语句时，父类初始化时的self.lastName为什么会调用子类的setter

SmithPerson *p1 = [[SmithPerson alloc] init];