gistfile1.php

<?php
class User {

public function getRoles()
    {
        if ($this->roles) {
            return $this->roles;
        }
        
        /** @var UserGroup[] $userGroups */
        $userGroups = $this->getGroups();

        $roles = [];
        foreach ($userGroups as $group) {
            $roles = array_merge($roles, $group->getRoles());
        }
        
        sort($roles);
        $this->roles = array_unique($roles);

        return $this->roles;
    }