OC之runtime(super)

对于下面的代码，打印的结果是啥

#import "LBStudent.h"

@implementation LBStudent

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

调用之后打印结果如下:

[self class] = LBStudent
[super class] = LBStudent
[self superclass] = LBPerson
[super superclass] = LBPerson

可以看到self和super调用class方法，打印的结果是一样的

将上面OC代码转成C++代码之后得到如下代码:

static instancetype _I_LBStudent_init(LBStudent * self, SEL _cmd) {
    self = ((LBStudent *(*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("LBStudent"))}, sel_registerName("init"));
    if (self) {
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_3q_7klqgj0j63z08zcx0skwjm500000gn_T_LBStudent_ad579e_mi_0, ((Class (*)(id, SEL))(void *)objc_msgSend)((id)self, sel_registerName("class")));
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_3q_7klqgj0j63z08zcx0skwjm500000gn_T_LBStudent_ad579e_mi_1, ((Class (*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("LBStudent"))}, sel_registerName("class")));
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_3q_7klqgj0j63z08zcx0skwjm500000gn_T_LBStudent_ad579e_mi_2, ((Class (*)(id, SEL))(void *)objc_msgSend)((id)self, sel_registerName("superclass")));
        NSLog((NSString *)&__NSConstantStringImpl__var_folders_3q_7klqgj0j63z08zcx0skwjm500000gn_T_LBStudent_ad579e_mi_3, ((Class (*)(__rw_objc_super *, SEL))(void *)objc_msgSendSuper)((__rw_objc_super){(id)self, (id)class_getSuperclass(objc_getClass("LBStudent"))}, sel_registerName("superclass")));
    }
    return self;
}

从上面代码可以看出，super其实调用的是self的objc_msgSendSuper,而class方法是类继承于NSObject时拥有的，class的方法伪代码实现大概如下:

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

class是返回消息接收者的类，super只是代表从父类中开始查找，消息接受者仍然是self