I'm just getting my feet wet in Wordpress, and I'm trying to write a very simple plugin using OOP techniques. I've been following this tutorial: http://www.yaconiello.com/blog/how-to-write-wordpress-plugin/ . So far I feel like I understand most of what's going on, but I'm slightly puzzled by statements such as this one:
add_action('init', array(&$this, 'init'));
Having read the documentation on Wordpress's add_action() and PHP callables, I gather that the second argument is a method of a class instance. But I don't understand why $this has to be passed by reference.
Found this note in the PHP docs about callables which I suspect may have something to do with it, but I'm still having a hard time wrapping my head around what the difference is:
Note: In PHP 4, it was necessary to use a reference to create a callback that points to the actual object, and not a copy of it. For more details, see References Explained.
If I have PHP 5, am I safe just using array($this,'init')?
Possibly related: add_action in wordpress using OOP?
Yes - you are safe to just use array($this, 'init');.
What this actually is, is a "callable" in PHP. It will be invoked using call_user_func() or call_user_func_array() (internally inside the add_action method).
PHP's official description of this type of callable:
A method of an instantiated object is passed as an array containing an object at index 0 and the method name at index 1.
You can read more about callables here.