Strong typed return value

[zhigang1992]

graphql-zeus was able to strong type return result will using pretty much the same syntax as this library. Would be nice to have that support as well.

[zhigang1992]

Here is a gist of it

export interface UserRequest {
  name?: boolean
  age?: boolean
  blogs?:
  | [{ first?: number }, BlogRequest]
  | BlogRequest
  __typename?: boolean
  __scalar?: boolean
}

export interface UserOutput {
  name: String
  age: number
  blogs: BlogOutput[];
  __typename: 'UserOutput'
}

export interface BlogRequest {
  title?: boolean;
  article?: boolean;
  createdAt?: boolean;
  __typename?: boolean
  __scalar?: boolean
}

export interface BlogOutput {
  title: string;
  article: string;
  createdAt: string;
  __typename: 'BlogOutput'
}

type Anify<T> = { [P in keyof T]?: any };

type LastMapTypeSRCResolver<Output, Filter> = Output extends undefined
  ? undefined
  : Output extends Array<infer AR>
  ? LastMapTypeSRCResolver<AR, Filter>[]
  : Filter extends boolean
  ? Output
  : MapType<Output, Filter>;

type MapType<Output extends Anify<Filter>, Filter> = Output extends boolean ? boolean : {
  [Key in keyof Filter]: Filter[Key] extends [any, infer PAYLOAD]
  ? LastMapTypeSRCResolver<Output[Key], PAYLOAD>
  : LastMapTypeSRCResolver<Output[Key], Filter[Key]>;
}

type Execute<Request, Output> = <Z extends Request>(subFields: Z) => MapType<Output, Z>

let execute: Execute<UserRequest, UserOutput>

const a = execute({ name: true, blogs: {title: true} });

a.name;

a.blogs[0].title;

a.age // type script complains 

But I don't have enough knowledge on this code base to create a PR yet.

[helios1138]

@zhigang1992 I tried something similar in the past but was not able to make it work for union/interface types and didn't have the time to work on it since. I will take a look how graphql-zeus managed to solve this issue.