gistfile1.php

<?php
// All of these will fail miserably:

class MyClass {
     function __construct() { }
}

// no function named MyClass
add_action( 'admin_init', 'MyClass' );

// not a callable value
$var = new MyClass();
add_action( 'admin_init', array( &$var ) );

// Plain heresey of the highest order, also it's non-working heresey 
add_action( 'admin_init', array( &$var, '__construct' ) );

// this isn't a callable value either
add_action( 'admin_init', 'MyClass::__construct' );