ReflectionClass::newInstanceWithoutConstructor()

(PHP 5 >= 5.4.0, PHP 7)

创建一个新的类实例而不调用它的构造函数

说明

publicReflectionClass::newInstanceWithoutConstructor(void): object

创建一个新的类的实例而不调用它的构造函数。

参数

返回值

更新日志

错误／异常

如果这个类是一个不能不调用构造函数来实例化的内置类，将导致一个ReflectionException。在 PHP 5.6.0 及更高版本中，此异常仅限于final的内置类。

参见

• ReflectionClass::newInstance() 从指定的参数创建一个新的类实例
• ReflectionClass::newInstanceArgs() 从给出的参数创建一个新的类实例。

It should be made clear that from an OOP theory perspective the use of this method is very bad practice in the same manner as goto, eval and singletons. If you find a need to use it in production code you're almost certainly doing something wrong somewhere. It may occasionally be useful for debugging, but even then hints at poor initial code.
The problem? It breaks encapsulation. An object can exist in the application but may not be able to fulfill its responsibility because it's missing dependencies. The use of this method makes it possible for an incomplete object to exist in the system; the object can exist in a state that its author never intended. This is bad because it will cause unexpected things to happen! A fundamental principle in OOP is that objects are in complete control of their state, the use of this method prevents that guarantee. 
n.b. The annotation based "dependency injection" listed below is not a solution or valid use-case for this either because it breaks encapsulation (Among other things!) and the class being constructed needs to know of the container by providing annotations.

If this method is not available in your version of PHP you can use a trick to create an instance without calling the constructor.
Use reflection to get the properties and default values of the class, and create a fake "serialized" string. 
<?php
function createInstanceWithoutConstructor($class){
  $reflector = new ReflectionClass($class);
  $properties = $reflector->getProperties();
  $defaults = $reflector->getDefaultProperties();
      
  $serealized = "O:" . strlen($class) . ":\"$class\":".count($properties) .':{';
  foreach ($properties as $property){
    $name = $property->getName();
    if($property->isProtected()){
        $name = chr(0) . '*' .chr(0) .$name;
      } elseif($property->isPrivate()){
        $name = chr(0) . $class. chr(0).$name;
      }
      $serealized .= serialize($name);
      if(array_key_exists($property->getName(),$defaults) ){
        $serealized .= serialize($defaults[$property->getName()]);
      } else {
        $serealized .= serialize(null);
      }
    }
  $serealized .="}";
  return unserialize($serealized);
}
?>
Example:
<?php
class foo
{
  public $a = 10;
  protected $b = 2;
  private $c = "default";
  protected $d;
  public function __construct(){
    $this->a = null;
    $this->b = null;
    $this->c = "constructed";
    $this->d = 42;
  }
}
var_dump(createInstanceWithoutConstructor('foo'));
?>
Output:
object(foo)#6 (4) {
 ["a"]=>
 int(10)
 ["b":protected]=>
 int(2)
 ["c":"foo":private]=>
 string(7) "default"
 ["d":protected]=>
 NULL
}
I hope this can help someone.
Oliver Anan

sorry for replying to such an old comment, but there's something i wanted to point out.
@ tom at r dot je:
While I agree with what you said in general, there *are* cases where it's not true, and since PHP doesn't allow for multiple constructors there's no other good way around it.
> The problem? It breaks encapsulation. 
> An object can exist in the application but may not be able to fulfill its 
> responsibility because it's missing dependencies. 
> The use of this method makes it possible for an incomplete object 
> to exist in the system; 
> the object can exist in a state that its author never intended.
If you're using this method from some factory method, to manually init the object in other way that the constructor that, this point is no longer valid.
Consider the example, where you use constructor to set-up the object after getting it from database (e.g. you need to pull some array from other table, basing on some id parameter). But you want to also be able to create object manually (for inserting to the database, for example).
The best thing to do would be to have two different constructors, but since it is not possible in php you need some other way to create the object.
example:
<?php
// this usually would be a static cache in some class, or array returned by method getMeta($id), etc.
$meta = array(1337 => array('key1' => 'value1', 'key2' => 'value2'));
class Test {
  public $id;
  public $data;
  public $meta;
  public function __construct() {
    global $meta;
    if(is_int($this->id)) $this->meta = $meta[$this->id];
  }
  public static function create_empty() {
    $r = new ReflectionClass(__CLASS__);
    return $r->newInstanceWithoutConstructor();
  }
}
echo "emulating PDO::FETCH_CLASS behavior: ";
$t = Test::create_empty();
$t->meta = 1337;
$t->__construct();
var_dump($t);
echo "empty class: ";
$testItem = Test::create_empty();
// ... here you can start setting up the item, e.g. from XML
var_dump($testItem);
$testItem->id = 0;
$testItem->data = "some data";
$testItem->meta = array("somekey" => "somevalue");
echo "after setup:";
var_dump($testItem);
?>
Of course, you can instead make empty constructor, and create some init() method, but then you have to remember to call init() everywhere.
You can also create some other way of adding the item to database, but then you'd have to classes to handle the same data - one for retrieving and other for storing.
If you instead use some factory class (or just a factory method, like in the simplified example above) having a way to create totally empty object is useful. With full factory approach you would first use some TestFactory->prepare() method, then you'd call methods to set what you need, and the factory would set all uninitialized variables to some default values upon calling TestFactory->get() to retrieve prepared object.

A good first use for this new method.
It implements a transparent parser constructor argument to achieve 99% reusable component.
<?php
use ReflectionClass ;
trait TSingleton
{
  /**
  *  Constructor.
  */
  protected function __construct() {}
  /**
  *  Drop clone singleton objects.
  */
  protected function __clone() {}
  /**
  *  Gets only one instance.
  *
  *  @params Optional multiple values as arguments for the constructor.
  *  @return Object instance from called class.
  */
  public static function getInstance()
  {
    static $instance = null ;
    if ( ! $instance )
    {
      $ref = new ReflectionClass( get_called_class() ) ;
      $ctor = $ref->getConstructor() ;
      // Thanks PHP 5.4
      $self = $ref->newInstanceWithoutConstructor() ;
      // The magic.
      $ctor->setAccessible( true ) ;
      $instance = $ctor->invokeArgs( $self, func_get_args() ) ;
    }
    return $instance ;
  }
}
?>

This new Feature enables Annotation based Dependency Injection:
<?php 
//dependency to inject
class dep {}
class a {
 /**
  * @inject
  * @var dep
  */
 protected $foo;
}
class b extends a {
 /**
  * @inject
  * @var dep
  */
 protected $bar;
 
 public function __construct() {
  echo "CONSTRUCTOR CALLED\n";
 }
}
$ref = new ReflectionClass('b');
$inst = $ref->newInstanceWithoutConstructor();
 
$list = $ref->getProperties();
foreach($list as $prop){
 /* @var $prop ReflectionProperty */
 $prop->getDocComment(); //grep for @inject and the @vars class name
 $prop->setAccessible(true);
 $prop->setValue($inst, new dep());
}
if($const = $ref->getConstructor()) {
 $constName = $const->getName();
 $inst->{$constName}(); //use call_user_func_array($function, $param_arr); for arguments 
}
print_r($inst);
print_r($inst->foo); //property still not accessable
The Output:
CONSTRUCTOR CALLED
b Object
(
  [bar:protected] => dep Object
    (
    )
  [foo:protected] => dep Object
    (
    )
)
PHP Fatal error: Cannot access protected property b::$foo in diTest.php on line 42