Laravel Lighthouse Where to place non root field resolvers?

In the example in the documentation of lighthouse they give a example method for resolving non-root fields.

<?php

use App\Models\User;

function resolveUserId(User $user): string
{
    return $user->name; // test...
}

So my guess is that lighthouse will search for a resolveUser{Field} method, and call it if it exists. But where do I place the method? there's no class name or namespace in the example.

type Query @guard(with: ["api"]) { me: User! @auth }

type User {
    id: ID!
    name: String!
    email: String!
    posts (content_contains: [String]): [Post!]! @hasMany #Would like to be able to resolve content_contains somehow...
    created_at: DateTime!
    updated_at: DateTime!
}

Documentation URL:

https://lighthouse-php.com/4.9/the-basics/fields.html#resolving-non-root-fields