Typescript类型体操 - IsNever

题目

中文

实现一个以 T 作为泛型参数的 IsNever类型.
如果 T 是never, 返回 true, 否则返回 false.
示例:

1. type A = IsNever<never>; // expected to be true
2. type B = IsNever<undefined>; // expected to be false
3. type C = IsNever<null>; // expected to be false
4. type D = IsNever<[]>; // expected to be false
5. type E = IsNever<number>; // expected to be false

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English

Implement a type IsNever, which takes input type T.
If the type of resolves to never, return true, otherwise false.
For example:

1. type A = IsNever<never>; // expected to be true
2. type B = IsNever<undefined>; // expected to be false
3. type C = IsNever<null>; // expected to be false
4. type D = IsNever<[]>; // expected to be false
5. type E = IsNever<number>; // expected to be false

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答案

1. type IsNever<T extends unknown> = [T] extends [never] ? true : false;

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