structs.php

<?php

declare(strict_types=1);

namespace App;

struct User {
  string $identifier;
}

struct PasswordAuthenticated {
  string $password;
}

struct SecurityUser extends User, PasswordAuthenticated {
  array $roles = ['user'];
}

$first = SecurityUser { identifier: 'foo', password: 'bar' };
var_dump($first->roles); // ['user'], pre-defined

$user = SecurityUser { identifier: 'foo', password: 'bar', roles: ['user', 'admin'] };
var_dump($user->roles); // ['user', 'admin'], defined in initliaztion 

$other = $user with { identifier: 'bar' };

/**
 * @template T of User
 * @param T $user
 * @return T
 */
function foo(User $user): User {
  echo $user->identifier;
  
  return $user with { identifier: 'baz' };
}

$other = foo($other);
assert($other instanceof SecurityUser);

// follows definition order, identifier, then password, then roles.
foreach($other as $column => $value) {
 echo "$column\n"; 
}

// output:
// identifier
// password
// roles