OC源码分析-Runtime源码分析(一)

一 : isa

用一个字节来描述三个bool值属性

取出特定位

& 对应想取的位 置为 1 ,转换成bool

代码优化

// 掩码，一般用来按位与(&)运算的
//#define MJTallMask 1
//#define MJRichMask 2
//#define MJHandsomeMask 4

//#define MJTallMask 0b00000001
//#define MJRichMask 0b00000010
//#define MJHandsomeMask 0b00000100

#define MJTallMask (1<<0)
#define MJRichMask (1<<1)
#define MJHandsomeMask (1<<2)

- (BOOL)isTall
{
    return !!(_tallRichHansome & MJTallMask);
}
- (BOOL)isRich
    {
        return !!(_tallRichHansome & MJRichMask);
    }


- (BOOL)isHandsome
{
    return !!(_tallRichHansome & MJHandsomeMask);
}

设置值

- (void)setTall:(BOOL)tall
{
    if (tall) {
        _tallRichHansome |= MJTallMask;
    } else {
        _tallRichHansome &= ~MJTallMask;
    }
}



- (void)setRich:(BOOL)rich
{
    if (rich) {
        _tallRichHansome |= MJRichMask;
    } else {
        _tallRichHansome &= ~MJRichMask;
    }
}

- (void)setHandsome:(BOOL)handsome
{
    if (handsome) {
        _tallRichHansome |= MJHandsomeMask;
    } else {
        _tallRichHansome &= ~MJHandsomeMask;
    }
}

结构体位域

@interface MJPerson()
{
    // 位域
    struct {
        char tall : 1;
        char rich : 1;
        char handsome : 1;
    } _tallRichHandsome;
}
@end

结构体位域取值与赋值

@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;
}

二 : 共用体

这里结构体是一个摆设,增加可读性,不影响值

#define MJTallMask (1<<0)
#define MJRichMask (1<<1)
#define MJHandsomeMask (1<<2)
#define MJThinMask (1<<3)

@interface MJPerson()
{
    union {
        char bits;
        
        struct {
            char tall : 1;
            char rich : 1;
            char handsome : 1;
            char thin : 1;
        };
    } _tallRichHandsome;
}
@end

@implementation MJPerson

- (void)setTall:(BOOL)tall
{
    if (tall) {
        _tallRichHandsome.bits |= MJTallMask;
    } else {
        _tallRichHandsome.bits &= ~MJTallMask;
    }
}

- (BOOL)isTall
{
    return !!(_tallRichHandsome.bits & MJTallMask);
}

- (void)setRich:(BOOL)rich
{
    if (rich) {
        _tallRichHandsome.bits |= MJRichMask;
    } else {
        _tallRichHandsome.bits &= ~MJRichMask;
    }
}

- (BOOL)isRich
{
    return !!(_tallRichHandsome.bits & MJRichMask);
}

- (void)setHandsome:(BOOL)handsome
{
    if (handsome) {
        _tallRichHandsome.bits |= MJHandsomeMask;
    } else {
        _tallRichHandsome.bits &= ~MJHandsomeMask;
    }
}

- (BOOL)isHandsome
{
    return !!(_tallRichHandsome.bits & MJHandsomeMask);
}



- (void)setThin:(BOOL)thin
{
    if (thin) {
        _tallRichHandsome.bits |= MJThinMask;
    } else {
        _tallRichHandsome.bits &= ~MJThinMask;
    }
}

- (BOOL)isThin
{
    return !!(_tallRichHandsome.bits & MJThinMask);
}

@end