Using php magic setters and getters to validate object properties

magic.php

<?php
date_default_timezone_set('America/Sao_Paulo');

/**
 * Classe com filtros mágicos sobre as propriedades
 */
abstract class Magic {
  
	/** @var array Propriedades */
	private $_properties;
	
	/**
	 * Construtor, armazena e remove de si as propriedades
	 */
	public function __construct() {
		foreach($this as $key => $value) {
			if($key != '_properties') {
				unset($this->$key);
				$this->_properties[$key] = $value;
			}
		}
	}
	
	/**
	 * Obtém uma propriedade
	 * @param string $key
	 * @return unknown_type
	 */
	public function __get($key) {
		return $this->_properties[$key];
	}
	
	/**
	 * Armazena uma propriedade
	 * @param string $key
	 * @param unknown_type $value
	 */
	public function __set($key, $value) {
		$this->_properties[$key] = $value;
	}
}

/**
 * Representa um usuário
 */
class User extends Magic {
	public $name;
	public $role;
	public $email;
	public $created;
	
	/**
	 * Roda ao construir
	 */
	public function __construct() {
		parent::__construct();
		
		// preenche campos padrão
		$this->created = new DateTime;
		$this->role = 'user';
	}
	
	/**
	 * Roda ao armazenar
	 * @param string $key
	 * @param unknown_type $value
	 */
	public function __set($key, $value) {
		
		// datetime
		if($key == 'created' && (!$value instanceof DateTime))
			throw new Exception('Field '.$key.' should contain instance of DateTime');
		
		// email
		if($key == 'email' && !strpos($value, '@'))
			throw new Exception('Field '.$key.' should contain a valid email');
		
		// prossegue
		parent::__set($key, $value);
	}
	
	/**
	 * Roda ao obter
	 * @param string $key
	 * @return unknown_type $value
	 */
	public function __get($key) {
		$value = parent::__get($key);
		
		// required
		if(in_array($key, array('name', 'email', 'role')) && empty($value))
			throw new Exception('Required field '.$key.' can not be empty');
		
		// format
		if($key == 'created')
			$value = $value->format('Y-m-d H:i:s');
		
		// prossegue
		return $value;
	}
}

$u = new User();
$u->name = 'Manolo';
$u->email = 'manolo@server';

echo '<pre>User:'."\n";
echo '    name: '.$u->name."\n";
echo '    role: '.$u->role."\n";
echo '    email: '.$u->email."\n";
echo '    created: '.$u->created."\n";