objective-c - iOS中getter/setter的問題

Question

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

以上在子類別SmithPerson中沒有重寫lastName的getter/setter方法，我可以在init中透過self.lastName重新賦值，但是如果我在子類別中重寫了getter/setter，那怎麼重新賦值呢？ self.lastName會呼叫子類別的setter方法，setter中如果這樣賦值就死循環了

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

另外：如果將Person和SmithPerson的init方法改成下面這樣，同時子類別重寫父類別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;
}

那麼執行下面語句時，父類別初始化時的self.lastName為什麼會呼叫子類別的setter

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

Answer 1

1、子類別重寫了getter/setter

@interface SmithPerson : Person

@end

@implementation SmithPerson

- (void)setLastName:(NSString *)lastName {
    [super setLastName:lastName];
}

@end

2、

self.lastName = @"abc";
//该方法等价于 [self setLastName:@"abc"];
//self 的类型为SmithPerson，所以会调用SmithPerson 类的 -setLastName: 方法