Apple 有时会在其应用程序中使用按位移位运算符enum定义。例如，在CGDirectDisplay.h文件是核心图形的一部分：
enum {
kCGDisplayBeginConfigurationFlag = (1 << 0),
kCGDisplayMovedFlag = (1 << 1),
kCGDisplaySetMainFlag = (1 << 2),
kCGDisplaySetModeFlag = (1 << 3),
kCGDisplayAddFlag = (1 << 4),
kCGDisplayRemoveFlag = (1 << 5),
kCGDisplayEnabledFlag = (1 << 8),
kCGDisplayDisabledFlag = (1 << 9),
kCGDisplayMirrorFlag = (1 << 10),
kCGDisplayUnMirrorFlag = (1 << 11),
kCGDisplayDesktopShapeChangedFlag = (1 << 12)
};
typedef uint32_t CGDisplayChangeSummaryFlags;
为什么不简单地使用递增int就像“正常”一样enum?
也许以十六进制（或二进制）写入值会有所帮助:-)
enum {
kCGDisplayBeginConfigurationFlag = (1 << 0), /* 0b0000000000000001 */
kCGDisplayMovedFlag = (1 << 1), /* 0b0000000000000010 */
kCGDisplaySetMainFlag = (1 << 2), /* 0b0000000000000100 */
kCGDisplaySetModeFlag = (1 << 3), /* 0b0000000000001000 */
kCGDisplayAddFlag = (1 << 4), /* 0b0000000000010000 */
kCGDisplayRemoveFlag = (1 << 5), /* 0b0000000000100000 */
kCGDisplayEnabledFlag = (1 << 8), /* 0b0000000100000000 */
kCGDisplayDisabledFlag = (1 << 9), /* 0b0000001000000000 */
kCGDisplayMirrorFlag = (1 << 10),/* 0b0000010000000000 */
kCGDisplayUnMirrorFlag = (1 << 11),/* 0b0000100000000000 */
kCGDisplayDesktopShapeChangedFlag = (1 << 12) /* 0b0001000000000000 */
};
现在您可以添加它们（或“或”它们）并获得不同的值
kCGDisplayAddFlag | kCGDisplayDisabledFlag /* 0b0000001000010000 */
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