捕获映射类型中的泛型参数

Question

在打字稿中，我想使用不属于签名的通用参数。例如，我想要一些类似下面的代码...

type NotArray<T> = T extends Array<I> ? I: T;
type Test1 = NotArray<Array<number>>; // Resolves to 'number'
type Test2 = NotArray<string>> // Resolves to 'string'

使用Cannot find name 'I'. 编译失败如果我将I 更改为any，它将编译，但解析的类型是any。例如：

type NotArray<T> = T extends Array<any> ? any: T;
type Fail = NotArray<Array<number>>; // Resolves to 'any'

有没有办法将泛型参数“捕获”到数组中？

Answer 1

只需在I 定义之前添加infer 关键字：

type NotArray<T> = T extends Array<infer I> ? I: T;
type Test1 = NotArray<Array<number>>; // Resolves to 'number'
type Test2 = NotArray<string> // Resolves to 'string'

见Type inference in conditional types