How do I call the parent classes constructor with its original parameters in PHP

Question

I have this code:

class A {
  var $arr = array();

  function __construct($para) {
    echo 'Not called';
  }
}

class B extends A {
  function __construct() {
    $arr[] = 'new Item';
  }
}

And as B has its own constructor construct($para) of A never gets called.

Now I could call parent::__construct($para) but then class B would need to be aware of the parameters class A needs.

I would prefer this:

class A {
  var $arr = array();

  function __construct($para) {
    echo 'Not called';
  }
}

class B extends A {
  function __construct() {
    parent::__construct(); // With the parameters class B was created.

    // Additional actions that do not need direct access to the parameters
    $arr[] = 'new Item';
  }
}

Would something like that work?

I don't like the fact, that all classes that extend class A would need to define a new constructor, once class A changes its parameters, where all I want them to do is call the constructor of class A like when class B does not overwrite it with an own __construct() method.

Answer 1

There is a way to do this almost exactly like you originally described it, by using the call_user_func_array() and func_get_args() functions:

class B extends A {
    function __construct() {
        // call the parent constructor with whatever parameters were provided
        call_user_func_array(array('parent', '__construct'), func_get_args());

        // Additional actions that do not need direct access to the parameters
        $arr[] = 'new Item';
    }
}

While it makes an interesting exercise, I personally would not recommend actually using this - I think using a separate init() method is a much better design.