如果我想希望使用某种类型声明的子类型作为某个变量声明的类型…

typescript">export interface Car {
    Name: string;
    Speed: number;
    Manufactured: number;
}

const Speed: Car.Speed = 200;

上面的写法会抛出错误

Cannot access ‘Car.Speed’ because ‘Car’ is a type, but not a namespace. Did you mean to retrieve the type of the property ‘Speed’ in ‘Car’ with ‘Car[“Speed”]’

这是因为你的使用姿势不对。需要用如下的写法

typescript">const Speed: Car['Speed'] = 200;

这种类型称为Lookup Types

这种使用某种类型的"成员类型"作为类型声明的使用有两种方式：

typescript">interface Person {
  name: string;
  age: number;
  location: string;
}

type K1 = keyof Person; // "name" | "age" | "location"
type K2 = keyof Person[]; // "length" | "push" | "pop" | "concat" | ...
type K3 = keyof { [x: string]: Person }; // string

或者

typescript">type P1 = Person["name"]; // string
type P2 = Person["name" | "age"]; // string | number
type P3 = string["charAt"]; // (pos: number) => string
type P4 = string[]["push"]; // (...items: string[]) => number
type P5 = string[][0]; // string

参考：

https://stackoverflow.com/questions/55607608/how-can-i-reuse-a-type-of-an-interface-member