Iterating through object variables

Deep down in the heart of PHP, an object isn't really all that different from an array - an object has pointers to the functions of its class, sure, but otherwise it just stores variables. As a result, we can treat an object as an array with the foreach loop, and it will iterate through each of the variables inside that object - as long as they are accessible. That is, private and protected variables will not be accessible in the general scope. Take a look at this script:

<?php
    class person {
        public $FirstName = "Bill";
        public $MiddleName = "Terence";
        public $LastName = "Murphy";
        private $Password = "Poppy";
        public $Age = 29;
        public $HomeTown = "Edinburgh";
        public $FavouriteColour = "Purple";
    }

    $bill = new person();

    foreach($bill as $var => $value) {
        echo "$var is $value\n";
    }
?>

Save that script as arrayobject.php and try running it. Your output should be this:

Note that the $Password variable is nowhere in sight, because it is marked Private and we're trying to access it from the global scope. If we re-jig the script a little so that the foreach loop is called by the object, we should be able to see the variable:

<?php
    class person {
        public $FirstName = "Bill";
        public $MiddleName = "Terence";
        public $LastName = "Murphy";
        private $Password = "Poppy";
        public $Age = 29;
        public $HomeTown = "Edinburgh";
        public $FavouriteColour = "Purple";

        public function outputVars() {
            foreach($this as $var => $value) {
                echo "$var is $value\n";
            }
        }
    }

    $bill = new person();
    $bill->outputVars();
?>

Now the output is this:

Now that it's the object itself looping through its variables, we can see private variables just fine. Looping through objects this way is a great way to hand-write serialization functions - just remember to put the function inside the object, otherwise private and protected data will get ignored!

Copyright ©2015 Paul Hudson. Follow me: @twostraws.