Super

@interface person : NSObject

@end

@interface student : person

@end

@implementation student

- (instancetype)init
{
    self = [super init];
    if (self) {
        
        NSLog(@"%@---\n",[self class]);
        NSLog(@"%@---\n",[self superclass]);
        NSLog(@"%@---\n",[super class]);
        NSLog(@"%@---\n",[super superclass]);
    }
    return self;
}

@end

 Super[2393:41718] student---
 Super[2393:41718] person---
 Super[2393:41718] student---
 Super[2393:41718] person---

先写个run方法 student继承然后重写,编译为c++文件.

- (void)run{
    [super run];

    ((void (*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("student"))}, sel_registerName("run"));
}

super 被转换成 objc_msgSendSuper,里面包含了一个objc_super的结构体.

/// Specifies the superclass of an instance. 
struct objc_super {
    __unsafe_unretained _Nonnull id receiver;
    __unsafe_unretained _Nonnull Class super_class;
};

/** 
 * Sends a message with a simple return value to the superclass of an instance of a class.
 * 
 * @param super A pointer to an \c objc_super data structure. Pass values identifying the
 *  context the message was sent to, including the instance of the class that is to receive the
 *  message and the superclass at which to start searching for the method implementation.
 * @param op A pointer of type SEL. Pass the selector of the method that will handle the message.
 * @param ...
 *   A variable argument list containing the arguments to the method.
 * 
 * @return The return value of the method identified by \e op.
 * 
 * @see objc_msgSend
 */
OBJC_EXPORT id _Nullable
objc_msgSendSuper(struct objc_super * _Nonnull super, SEL _Nonnull op, ...)
    OBJC_AVAILABLE(10.0, 2.0, 9.0, 1.0, 2.0);

objc_super 有2个成员,一个是消息接收者,一个父类, objc_msgSendSuper方法是从父类的方法列表开始寻找.消息接收者还是self.而class的方法实现都是NSObject,查看源码实现:

- (Class)class{
    return object_getClass(self);
}

- (Class)superclass{
    return class_getSuperclass(object_getClass(self));
}

所有无论是[sefl class]还是[ super class],输出的都是student;

ex: isKindOfClass 和 isMemberOfClass

+ (Class)class {
    return self;
}

- (Class)class {
    return object_getClass(self);
}

+ (Class)superclass {
    return self->superclass;
}

- (Class)superclass {
    return [self class]->superclass;
}

+ (BOOL)isMemberOfClass:(Class)cls {
    return object_getClass((id)self) == cls;
}

- (BOOL)isMemberOfClass:(Class)cls {
    return [self class] == cls;
}

+ (BOOL)isKindOfClass:(Class)cls {
    for (Class tcls = object_getClass((id)self); tcls; tcls = tcls->superclass) {
        if (tcls == cls) return YES;
    }
    return NO;
}

- (BOOL)isKindOfClass:(Class)cls {
    for (Class tcls = [self class]; tcls; tcls = tcls->superclass) {
        if (tcls == cls) return YES;
    }
    return NO;
}

        NSLog(@"%d----\n",[[NSObject class]isKindOfClass:[NSObject class]]);
        NSLog(@"%d----\n",[[NSObject class]isMemberOfClass:[NSObject class]]);
        NSLog(@"%d----\n",[[student class]isKindOfClass:[student class]]);
        NSLog(@"%d----\n",[[student class]isMemberOfClass:[student class]]);
        

[NSObject class]isKindOfClass:[NSObject class]]

• 左边返回一个类对象,右边遍历基类,而基类的superclass 是指向类对象的.所以返回1.

[[NSObject class]isMemberOfClass:[NSObject class]]);
[[student class]isKindOfClass:[student class]])
[student class]isMemberOfClass:[student class]])

• 类对象 != 基类