偶然發現NSArray的count屬性跟-1比較結果出人意料，見程式碼

NSArray *array=[NSArray new];
bool flag= array.count>-1;//false

@property (readonly) NSUInteger count;

NSUInteger的定義如下：

#if __LP64__ || (TARGET_OS_EMBEDDED && !TARGET_OS_IPHONE) || TARGET_OS_WIN32 || NS_BUILD_32_LIKE_64
typedef long NSInteger;
typedef unsigned long NSUInteger;
#else
typedef int NSInteger;
typedef unsigned int NSUInteger;
#endif
 

flag= (NSInteger)array.count>-1;//true
flag= (long)array.count>-1;//true
flag= (int)array.count>-1;//true