As with other programming languages, you can easily extend classes and objects:


<?php
class a {

    function __construct() {
        // this gets called in php5.
        echo "I am in function " . __FUNCTION__ . " of class " . __CLASS__ . "<br/>";
    }

    function a() {
        // this gets called in php4.
        // we'll have to call the constructor ourselves.
        $this->__construct();
    }
}

class b extends a {
}

$my_class = new b();

?>


The 'extends' keyword means 'class b' inherits all of 'class a' properties and methods (methods are simply 'functions' inside a class).

We haven't actually defined anything in 'class b' yet - so php will go back to 'class a' to see what we need to do.

If you run this through your browser you will see:

I am in function __construct of class a