<?php
    /**
     *
     */
    class PropertyTest
    {
        // Location for overload data
        private $data = array();

        // Overloading not used on declared properties
        public $declared = 1;

        // Overloading onnly used on this when accessed outside the class
        private $hidden = 2;

        public function __set($name, $value)
        {
            echo "Seeting '$name' to '$value'\n";
            $this->data[$name] = $value;
        }

        public function __get($name)
        {
            echo "Getting '$name'\n";
            if (array_key_exists($name, $this->data)) {
                return $this->data[$name];
            }

            $trace = debug_backtrace();
            trigger_error(
                'Undefined property via __get();'.$name.
                'in'.$trace[0]['file'].
                'on line'.$trace[0]['line'],
                E_USER_NOTICE
            );
            return null;
        }

        // As of PHP 5.1.0
        public function __isset($name)
        {
            echo "Is '$name' set?\n";
            return isset($this->data[$name]);
        }

        // As of PHP 5.1.0
        public function __unset($name)
        {
            echo "Unsetting '$name'\n";
            unset($this->data[$name]);
        }

        // Not a magic method, just here for example
        public function getHidden()
        {
            return $this->hidden;
        }
    }

    echo "<pre>\n";

    $obj = new PropertyTest;

    $obj->a = 1;
    echo $obj->a."\n\n";

    var_dump(isset($obj->a));
    unset($obj->a);
    var_dump(isset($obj->a));
    echo "\n";

    echo $obj->declared."\n\n";

    echo "Let's experiment with the private property named 'hidden':\n";
    echo "Privates are visible inside the class, so __get() not used...\n";
    echo $obj->getHidden()."\n";
    echo "Privates not visible outside the class, so __get() is used...\n";
    echo $obj->hidden."\n";
?>