CODEWITHSUNDEEP
typescript
Sergei Krivochenko
Sergei Krivochenko

Reputation: 637

How correct use generics?

There is a set of interfaces:

export interface FormData<T extends ControlData = any> {
  [type: string]: T;
}

export type FormResult<T extends FormData> = {
  [type in keyof T]: T[type];
};

export interface ControlData<T = any> {
  value: T;
}

export interface ButtonSelectControlData<T> extends ControlData<T> {
  query: string;
}

export interface RoutesAddCityData extends FormData {
  cityId: ButtonSelectControlData<number>;
  routeId: ControlData<number>;
}

When I use FormResult:

(data: FormResult<RoutesAddCityData>) => {
  // ...
}

As expected I see in IDE that data.cityId has type ButtonSelectControlData<number> and data.routeId has type ControlData<number>. But I would like to see type number in both cases. Is it possible?

Upvotes: 0

Views: 40

Answers (1)

Karol Majewski
Karol Majewski

Reputation: 25820

If I understand correctly, you want the FormResult type to extract the underlying type parameters from ButtonSelectControlData and ControlData. If that's the case, then one possible solution is to create a conditional type:

type FormResult<T> = {
  [K in keyof T]: T[K] extends ControlData<infer U>
    ? U
    : never         
}

Upvotes: 1

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