Runtime之super面试题

#import <Foundation/Foundation.h>
// 声明
@interface DXPerson : NSObject

@end

@implementation DXPerson

@end

@interface DXStudent : DXPerson

@end

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

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

[self class] = DXStudent
[self superclass] = DXPerson
--------------------------------
[super class] = DXStudent
[super superclass] = DXPerson

struct objc_super {
    __unsafe_unretained _Nonnull id receiver; // 消息接收者
    __unsafe_unretained _Nonnull Class super_class; // 消息接收者的父类
};

struct objc_super arg = {self, [DXPerson class]};
objc_msgSendSuper({self, [DXPerson class]}, @selector(class));

// super调用的receiver仍然是DXStudent对象
// super指明,查找class方法从父类DXPerson类对象开始查找,而不是从本身DXStudent类对象
[super class]

#import <objc/runtime.h>

// 伪代码
- (Class)class{
    return object_getClass(self);
}
// 伪代码
- (Class)superclass{
    return class_getSuperclass(object_getClass(self));
}