TypeScript - 遍历字典类型中的类型并创建具有转换值的类型

Question

Note: This is not about runtime, we are talking purely about types here.

Suppose there are types: Alpha<T> , Beta<T> and an example type like type Data = {a: Alpha<number>; b: Beta<string>, c: Alpha<string> } type Data = {a: Alpha<number>; b: Beta<string>, c: Alpha<string> } I need to transform it to something like: {a: number; b: string; c: string } {a: number; b: string; c: string }

I know how to transform a single value, I have this implemented already, but I have no idea how could I iterate over a dictionary type with known properties and transform them. Is it even possible?

class Alpha<T> {
    private a: T;
}

class Beta<T> {
    private b: T;
}

// Extracts T from Alpha<T> or Beta<T> - already implemented
type GetClassParameterForAlphaBeta<T extends Alpha<any> | Beta<any>> =
    T extends Alpha<infer R>
    ? R : T extends Beta<infer R>
    ? R : unknown;

type Store = { [index: string]: Alpha<any> | Beta<any> }

// pseudo-code to give you an idea of what I'm after
type GetStoreData<T extends Store> = T each U : GetClassParameterForAlphaBeta<U>;

type Data = {a: Alpha<number>; b: Beta<string>, c: Alpha<string> }

type x = GetStoreData<Data> // Expected: {a: number; b: string, c: string }

One thing to note is that the 2 classes are known, but Data in the real case is a generic. It has a finite amount of properties, but it's all dynamic. Manually applying the transformations is out of question.

Answer 1

Ah, you're just looking for a mapped type :

type GetStoreData<T extends Store> = {
  [K in keyof T]: GetClassParameterForAlphaBeta<T[K]>
}

You can verify that it works as expected:

type X = GetStoreData<Data> 
/* type X = {
    a: number;
    b: string;
    c: string;
} */

Playground link to code