如何将元组类型转换为联合? [英] How to convert a tuple type to a union?

问题描述

如何将元组泛型类型映射到联合类型?

How to map a tuple generic type to a union type?

type NeededUnionType<T> = T[keyof T]; // Includes all the Array properties values
  
const value: NeededUnionType<[7, string]> = 2; // This should not be allowed (2 is the tuple length)

预期类型:7 |字符串

推荐答案

您可以通过 number 而不是 keyof T 来索引.keyof T 将包含元组对象的所有键，包括长度以及任何其他数组属性.

You can index by number instead of keyof T. keyof T will contain all keys of the tuple object which includes the length as well as any other array properties.

type NeededUnionType<T extends any[]> = T[number]; // Includes all the Array properties values

const value: NeededUnionType<[7, string]> = 2; // err value is 7 | string 

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