在CFRuntime源码中有如下的代码(删减了很多):
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;
}
一个函数,居然即返回了unsigned long
,又返回了bool
,且返回了对象。一下子就扩展了我的知识面,因此我写了如下的测试代码:
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];
// 代码1: 需要把此文件修改为不支持ARC的,才能进行转换
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;
// 代码2: 如果这里是int的话,会导致int溢出,会得不到正确的内存地址
return (uintptr_t)value;
}
}
}
@end
代码1: 需要把此文件修改为不支持ARC的,才能进行转换
代码2: 如果这里是int的话,会导致int溢出,会得不到正确的内存地址
一些知识的总结:
- OC对象和id 最后都是通过指针来表示的,而指针地址就是数字
- 64位机器,
int
不够用了,所以需要unsigned long