super

示例

#import "NSPerson.h"

@interface NSStudent : NSPerson

- (void)superTest;

@end

#import "NSStudent.h"

@implementation NSStudent

- (void)superTest
{
    NSLog(@"self_class:%@",[self class]);
    NSLog(@"self_superclass:%@",[self superclass]);
    NSLog(@"super_class:%@",[super class]);
    NSLog(@"super_superclass:%@",[super superclass]);
}

@end

#import "NSStudent.h"

int main(int argc, const char * argv[]) {
        
    NSStudent *student = [[NSStudent alloc] init];
    [student superTest];
    return 0;
}

//log
2020-08-27 23:59:48.669409+0800 runtime[14450:547436] self_class:NSStudent
2020-08-27 23:59:48.669912+0800 runtime[14450:547436] self_superclass:NSPerson
2020-08-27 23:59:48.670006+0800 runtime[14450:547436] super_class:NSStudent
2020-08-27 23:59:48.670052+0800 runtime[14450:547436] super_superclass:NSPerson
Program ended with exit code: 0

self

[self class]、[self superclass]调用流程

    ((Class (*)(id, SEL))(void *)objc_msgSend)((id)self, sel_registerName("class"));
    ((Class (*)(id, SEL))(void *)objc_msgSend)((id)self, sel_registerName("superclass"));

super

[super class]、[super superclass]调用流程

struct objc_super {
    id receiver;
    Class super_class;
};

id  objc_msgSendSuper(struct objc_super * _Nonnull super, SEL _Nonnull op, ...)

    ((Class (*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("NSStudent"))}, sel_registerName("class"));
    ((Class (*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("NSStudent"))}, sel_registerName("superclass"));

说明：super调用方法，本质是调用objc_msgSendSuper给对象发送消息

objc_msgSendSuper第一个参数struct objc_super * _Nonnull super是一个结构体，封装了消息接收者(receiver)和父类对象(super_class)

第二个参数是方法本身

通过源码可以看出，消息接收者receiver仍然是当前对象self ，suerper_class是当前对象类对象的父类，作用是查找方法时从父类开始查找

注意：转换成的c++代码与程序实际运行转换成的代码有出入.
实际运行过程中，是调用objc_msgSendSuper2, 第一个参数struct objc_super * _Nonnull super结构体内部的第二个成员变量就是当前类