Partial application in TypeScript - Pick

pick.ts

/**
 * Typing partial application in TypeScript!
 * 
 * Here's a "pick" function which takes some property names and returns a function which will pick those
 * from an object passed to it.
 */
export function pick<T extends string>(props: T[]): <U>(input: U) => { [K in T]: K extends keyof U ? U[K]: never } {
    return {} as any; // implementation not important for now
}

interface Person {
    name: string;
    age: number;
    friends: Person[]
}

interface Dog {
    name: string;
    breed: string;
    friends: Dog[];
}

interface Cat {
    name: string;
}

let joe: Person = {} as any;
let fido: Dog = {} as any;
let felix: Cat = {} as any;

const pickFriends = pick(['friends']);