lazy.php

<?php

class User
{
    public $id;
    public $username;
    public $email;
}

$user = new User();
$user->id = 1234;

register_lazy_listener($user, ['username', 'email], function ($object, $lazyProperties, $accessedProperty) {
    $sql = 'SELECT username, email FROM user WHERE id = ?';
    $stmt = $pdo->prepare($sql);
    $stmt->bindParam(1, $object->id);
    $stmt->execute();
    
    $row = $stmt->fetch(PDO::FETCH_ASSOC);
    // $row with {"username": "user1234", ..."} for id: 1234
    
    $object->username = $row['username'];
    $object->email = $row['email'];

    return LAZY_UNREGISTER; // LAZY_KEEP? or always unregister when accessed?
});

echo $user->username; // makes magic sql query and prints "user1234"
echo $user->email; // no magic anymore here, the property is initialized