iOS底层学习-day-11
前言-OC-Rutime篇
我是一名iOS开发者， iOS底层 菜鸟的进阶之路30天。
isa指针
- 要想学习Runtime，首先要了解它底层的一些常用数据结构，比如isa指针
- 在arm64架构之前，isa就是一个普通的指针，存储着Class、Meta-Class对象的内存地址
- 从arm64架构开始，对isa进行了优化，变成了一个共用体（union）结构，还使用位域来存储更多的信息
位域
- MJPerson.h
#import <Foundation/Foundation.h>
@interface MJPerson : NSObject
- (void)setTall:(BOOL)tall;
- (void)setRich:(BOOL)rich;
- (void)setHandsome:(BOOL)handsome;
- (BOOL)isTall;
- (BOOL)isRich;
- (BOOL)isHandsome;
@end
- MJPerson.m
#import "MJPerson.h"
#define MJTallMask (1<<0) 0b 0000 0001
#define MJRichMask (1<<1) 0b 0000 0010
#define MJHandsomeMask (1<<2) 0b 0000 0100
@interface MJPerson()
{
char _tallRichHansome;
}
@end
@implementation MJPerson
- (instancetype)init {
if (self = [super init]) {
_tallRichHansome = 0b00000100;
}
return self;
}
- (void)setTall:(BOOL)tall {
if (tall) {
_tallRichHansome = _tallRichHansome | MJTallMask;
} else {
_tallRichHansome = _tallRichHansome & ~MJTallMask;
}
}
- (BOOL)isTall {
return !!(_tallRichHansome & MJTallMask);
}
- (void)setRich:(BOOL)rich {
if (rich) {
_tallRichHansome |= MJRichMask;
} else {
_tallRichHansome &= ~MJRichMask;
}
}
- (BOOL)isRich {
return !!(_tallRichHansome & MJRichMask);
}
- (void)setHandsome:(BOOL)handsome {
if (handsome) {
_tallRichHansome |= MJHandsomeMask;
} else {
_tallRichHansome &= ~MJHandsomeMask;
}
}
- (BOOL)isHandsome {
return !!(_tallRichHansome & MJHandsomeMask);
}
@end
优化后
- MJPerson.h
#import <Foundation/Foundation.h>
@interface MJPerson : NSObject
- (void)setTall:(BOOL)tall;
- (void)setRich:(BOOL)rich;
- (void)setHandsome:(BOOL)handsome;
- (BOOL)isTall;
- (BOOL)isRich;
- (BOOL)isHandsome;
@end
- MJPerson.m
#import "MJPerson.h"
@interface MJPerson()
{
// 位域
struct {
char tall : 1;
char rich : 1;
char handsome : 1;
} _tallRichHandsome; //0b 0000 0 handsome rich tall
}
@end
@implementation MJPerson
- (void)setTall:(BOOL)tall {
_tallRichHandsome.tall = tall;
}
- (BOOL)isTall {
return !!_tallRichHandsome.tall;
}
- (void)setRich:(BOOL)rich {
_tallRichHandsome.rich = rich;
}
- (BOOL)isRich {
return !!_tallRichHandsome.rich;
}
- (void)setHandsome:(BOOL)handsome {
_tallRichHandsome.handsome = handsome;
}
- (BOOL)isHandsome {
return !!_tallRichHandsome.handsome;
}
@end
isa_max
- 从arm64后，优化了isa，isa是 &isa_max才是指向对象的地址值的，采取共用体的结构，将一个64的结构体数据来储存更多东西，其中的shift_cls33位才是来储存具体的地址值的