因为[Distributive Conditional Types](https://link.segmentfault.com/?enc=zvS8YrYCmi6FQLDFYGflSQ%3D%3D.ezfeZn2Cfh6CUVN0AMsZBrSVkcQM6n02blTt4WpTjLnVmZEjy1%2BThhEdSD6B54S966iEuCT%2F56sFfgy%2BcUCWT4xbk93QtEpFYZTRyE%2B3ABEap39JCINOuo4%2FURk8ftm8KyDI%2B38xSk%2BB9HUvwLU1%2BA%3D%3D) // 所以 type res2 = MyExclude 相当于 type res2 = ('a' extends a ? never : 'a') | ('b' extends a ? never : 'b') | ('c' extends a ? never : 'c')