// Makes specified keys K of type T non-nullable
type NonNullableProperties<T, K extends keyof T> = {
  [P in keyof T]: P extends K ? NonNullable<T[P]> : T[P];
};

interface UserProfile {
  id: string;
  email?: string | null;
  phone?: string | null;
  age: number | undefined;
  address: {
    street: string;
    city: string;
  };
}

// Example: Make 'email' and 'phone' non-nullable
type CleanUserProfile = NonNullableProperties<UserProfile, 'email' | 'phone'>;

const user: CleanUserProfile = {
  id: 'user-123',
  email: 'test@example.com', // Must be string, not null/undefined
  phone: '123-456-7890',     // Must be string, not null/undefined
  age: 30,
  address: {
    street: '123 Main St',
    city: 'Anytown'
  }
};

// Error: Type 'null' is not assignable to type 'string'.
// const invalidUser: CleanUserProfile = {
//   id: 'user-124',
//   email: null,
//   phone: '123-456-7890',
//   age: 25,
//   address: { street: '456 Elm St', city: 'Otherville' }
// };

// console.log(user);