types

types.ts

interface ExampleQuery {
  name?: string;
  age?: number;
  child?: {
    id?: number;
    name?: string;
  };
}

const GET = Symbol();

/** Recursively map `T` such that all primitive properties become of type GET or their original type. */
type QueryForm<T> = {
  [K in keyof T]: (T[K] extends object ? (QueryForm<T[K]>) : (T[K] | typeof GET))
};

/** Recursively filter `T` by the keys of `S`. */
type DeepFilterBy<T, S> = { [K in (keyof S & keyof T)]: (T[K] extends object ? (DeepFilterBy<T[K], S[K]>) : (S[K] extends typeof GET ? T[K] : S[K])) };

/**
 * Submit a query based on the given interface, returning the desired fields.
 * @param get Object matching the interface shape but where the requested fields
 * are given the value `true`.
 */
function query<S extends QueryForm<ExampleQuery>>(get?: S): DeepFilterBy<ExampleQuery, S>  {
  return;
}


const queryResponse = query({
  name: GET,
  child: {
    id: 234,
    name: GET
  }
});

queryResponse.name
queryResponse.child.id
queryResponse.age