在CFRuntime源碼中有如下的代碼(刪減了很多):
typedef unsigned long uintptr_t;
CF_EXPORT uintptr_t __CFDoExternRefOperation(uintptr_t op, id obj) {
uintptr_t count;
switch (op) {
case 300: // increment
case 350: // increment, no event
CFBasicHashAddValue(table, disguised, disguised);
if (__CFOASafe && op != 350) __CFRecordAllocationEvent(__kCFObjectRetainedEvent, obj, 0, 0, NULL);
return (uintptr_t)obj;
case 450: // decrement, no event
count = (uintptr_t)CFBasicHashRemoveValue(table, disguised);
return 0 == count;
case 500:
count = (uintptr_t)CFBasicHashGetCountOfKey(table, disguised);
return count;
}
return 0;
}
一個(gè)函數(shù),居然即返回了unsigned long
,又返回了bool
,且返回了對(duì)象。一下子就擴(kuò)展了我的知識(shí)面,因此我寫了如下的測試代碼:
typedef NS_ENUM(NSInteger, RXTMIntToIdType) {
RXTMIntToIdType_Int,
RXTMIntToIdType_Bool,
RXTMIntToIdType_Object,
};
@implementation RXTMIntToIdObject
- (void)test {
uintptr_t r1 = [self valueWithType:RXTMIntToIdType_Int];
uintptr_t r2 = [self valueWithType:RXTMIntToIdType_Bool];
uintptr_t r3 = [self valueWithType:RXTMIntToIdType_Object];
// 代碼1: 需要把此文件修改為不支持ARC的,才能進(jìn)行轉(zhuǎn)換
NSObject *o3 = (id)r3;
NSLog(@"%ld, %ld, %ld, %@", r1, r2, r3, o3);
}
- (uintptr_t)valueWithType:(RXTMIntToIdType)type {
switch (type) {
case RXTMIntToIdType_Int:
return 0;
case RXTMIntToIdType_Bool:
{
NSInteger random = arc4random() % 2;
return random == 0;
}
case RXTMIntToIdType_Object:
default:
{
NSString *str = @"Hello I'm a string";
id value = str;
// 代碼2: 如果這里是int的話,會(huì)導(dǎo)致int溢出,會(huì)得不到正確的內(nèi)存地址
return (uintptr_t)value;
}
}
}
@end
代碼1: 需要把此文件修改為不支持ARC的,才能進(jìn)行轉(zhuǎn)換
代碼2: 如果這里是int的話,會(huì)導(dǎo)致int溢出,會(huì)得不到正確的內(nèi)存地址
一些知識(shí)的總結(jié):
- OC對(duì)象和id 最后都是通過指針來表示的,而指針地址就是數(shù)字
- 64位機(jī)器,
int
不夠用了,所以需要unsigned long