Late Static Binding with PHP 5.3

Jesse — Mon, 06 Oct 2008 05:34:45 +0000

With the Alpha3 Release of PHP 5.3 out and about it’s looking like the much anticipated late static binding functionality is starting to solidify. Once I finally got PHP 5.3 running (see my previous post) I worked through creating an ActiveRecord-like class to see if I could make a PHP object do act in a similar way similar to Ruby’s Active Record.

Lets see where I ended up…

class ActiveRecord {
  public static function find($id){
    $called_class = get_called_class(); //a new function as of a2
    return new $called_class();
  }
  //A derived example to show the late static binding in action
  public static function testLSB(){
    return static::$table;
  }
}
class BasicModel extends ActiveRecord {
  public static $table = 'basicModel';
}
//Output examples
echo get_class(BasicModel::Find(1)); //Output - BasicModel
echo BasicModel::testLSB();          //Output - basicModel
echo BasicModel::$table;             //Output - basicModel

First place I saw the get_called_class() method was on the PHP Late Static Binding Manual Page

The above example is celarly a bit derived, but I’m quite excited at where this is heading. I still have a bit of work to do if I want to end up accessing all my models in the Rails/Active Record fashion.

$user = new User(1); //by passing a user id directly to the constructor
$user = User::Find(1); //by static::find();
$users = Users::FindAll(); //by static::findAL() returning an array of User objects.

I don’t see these requirements too difficult to achieve but it will require some trickery. The problem will lie if I decide to put all the database logic into static::Find(). If static::Find() returns a new instance of the class, and the constructor of each class blindly returns the results of a static::Find() call, it won’t work. The code below doesn’t work because a constructor can’t return a new object instance and $this can’t be reassigned (like you can in some languages).

public function __construct($id){
 if (is_array($id)){
    $this-&gt;data = $id;
  }else{
    $this = static::find($id); //fatal error, can't reassign $this
    return static::find($id); //also won't do anything useful
  }
}

From fist impressions I think the idea of using is_array() to check if the $id parameter is a good way for static::Find() to pass an array to the constructor without ending up in a loop. This suggests that there needs to be a similar check inside static::Find() to return only an array in some cases instead of a new object.

So I’ve come up with this idea to solve the above issue.

public function __construct($id){
 if (is_array($id))
    $this-&gt;data = $id;
 else
    $this-&gt;data = static::find($id,true); //static::find() returns an array;
}
public static function Find($id,$returnArray = false){
  $foundResults = insert_SQL_function_here();
  if ($returnArray === true)
    return $foundResults; //return basic array
  else{
    $called_class = get_called_class();
    return new $called_class($foundResults);
  }
}

I’m not 100% convinced this is the best way to solve this. Ideally I’d like a solution that didn’t require the checks in __construct() and static::find(), but this is a start, and it’s a a reasonable exercise in using LSB.

The Netocracy » late static binding

Late Static Binding with PHP 5.3

First place I saw the get_called_class() method was on the PHP Late Static Binding Manual Page