block5.ts

function getProperty<A, P extends (keyof A) >(obj: A, prop: P): A[P] {
    return obj[prop];
}

const user: User = {
   firstName: "Georges",
   lastName: "Abitbol",
   age: 43
}

const name: string = getProperty(user, "firstName");
const age: number = getProperty(user, "age");

// The following doesn't compile

//Type 'string' is not assignable to type 'number'
const age: string = getProperty(user, "age");

//Argument of type '"name"' is not assignable to parameter of type '"firstName" | "lastName" | "age"'.
const name: string = getProperty(user, "name");