.description

#import <Foundation/Foundation.h>

@interface Person : NSObject

@property int age;

@end

@implementation Person

// 类方法中不能访问成员变量

//+ (NSString *)description

- (NSString *)description

{

    return [NSString stringWithFormat:@"_age=%d", _age];

}

@end

// 1个错误

/*-------------------------牛B的分隔线-------------------------*/

.id、SEL、类对象

#import <Foundation/Foundation.h>

@interface Person : NSObject

- (void)test;

@property int age;

@end

@implementation Person

- (void)test

{

    // 会引发死循环错误

    //[self performSelector:_cmd];

}

@end

int main()

{

    // id后面不能加上*

    //id *p = [[Person alloc] init];

    id p = [[Person alloc] init];

    [p setAge:];

    // id类型的变量不能用点语法

    // p.age = 10;

    Class c = [Person class];

    // 类对象只能调用类方法，不能调用对象方法

    //[c test];

    return ;

}