00021-easy-includes

[yunliuyan]

Includes

by null @kynefuk

   

在类型系统里实现 JavaScript 的 Array.includes 方法，这个类型接受两个参数，返回的类型要么是 true 要么是 false。

例如：

type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`

[yunliuyan]

思路

number将元素遍历出来

代码实现

type Includes<T extends readonly any[], U extends any> = U extends T[number] ? true : false

type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`

[Janice-Fan]

type Includes<T extends readonly any[], P extends any> = {
    [k in T[number]]: true;
}[P] extends true ? true : false;

type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'Dio'> // expected to be `false`

[Naparte]

// 在类型系统里实现 JavaScript 的 Array.includes 方法，这个类型接受两个参数，返回的类型要么是 true 要么是 false。

type Includes<T extends any[], K> = K extends T[number] ? true : false;

type isPillarMen = Includes<['Kars', 'Esidisi', 'Wamuu', 'Santana'], 'xxx'> // expected to be `false`