Question

Working with a PHP library class, and I’d like to wrap all of its public functions in a subclass… Something along the lines of:

class BaseClass
{
   function do_something()
   {
        some;
        stuff;
   }

   function do_something_else()
   {
        other;
        stuff;
   }

   /*
    * 20-or-so other functions here!
    */
}

class SubClass extends BaseClass
{
   function magicalOverrideEveryone()
   {
        stuff-to-do-before;        // i.e. Display header
        call_original_function();  // i.e. Display otherwise-undecorated content
        stuff-to-do-after;         // i.e. Display footer
   }
}

Boiling it down, I’d prefer not to have to override every superclass method with the same wrapper code, if there’s a [somewhat elegant / clean] way to do it all in one place.

Is this possible? I suspect I’m in metaprogramming land here, and don’t even know if PHP offers such a beast, but figured I’d ask…

Answer 1

You could do this easily with the __call magic method and a generic “proxy” class which doesn’t inherit directly from the base class.

Here is a (near) complete implementation of a proxying class which wraps whatever object you pass it. It will invoke some “before” and “after” code around each method call.

class MyProxy {
  function __construct($object) {
    $this->object = $object;
  }

  function __call($method, $args) {
    // Run before code here

    // Invoke original method on our proxied object
    call_user_func_array(array($this->object, $method), $args);

    // Run after code here
  }
}


$base = new BaseClass();
$proxy = new MyProxy($base);

$proxy->doSomething(); // invoke $base->doSomething();

You would of course want to add a bit of error handling, like asking the proxied object if it responds to the given method in __call and raising an error if it doesn’t. You could even design the Proxy class to be a base-class for other proxies. The child proxy classes could implement before and after methods.

The downside is that your “child class” no longer implements BaseClass, meaning if you’re using type-hinting and want to demand that only objects of type BaseClass are passed into a function, this approach will fail.