<?php

class User
{
    protected $name;
    protected $surname;
    protected $password;

    public function setName($name)
    {
        $this->name = $name;
        return $this;
    }

    public function setSurname($surname)
    {
        $this->surname = $surname;
        return $this;
    }

    public function setPassword($password)
    {
        if (!$password) {
            throw new InvalidArgumentException("Password shouldn't be empty");
        }
        $this->password = $password;
        return $this;
    }
}

$user = new User;
$user->setName('John')->setSurname('Doe')->setPassword('root');
?>