typescript 如何理解never

Question

type T = '1' | '2'
type U = '1'

type N1 = T extends U ? never : T
type N2 = Exclude<T, U>

const n10: N1 = '1'
const n11: N1 = '2'

const n2: N2 = '2'

如上，对于 N1的类型是按着文档实现的，可与 Exclude 为什么表现不一致？

Answer 1

type N1<T, U> = T extends U ? never : T

const n10: N1<T, '1'> = '2'

N1要是泛型，同时在使用N1的时候确定具体类型