Question

This should be easy.. can someone explain the syntax for me?

I have a controller which instantiates a bootstrap class (new keyword) which instantiates the config class.

the controller then instantiates a startpage class which extends the bootstrap class. In the startpage class I’m trying to access the config object in the bootstrap (parent) class.

Can this even be done? Or does startpage have to instantiate bootstrap directly? Does instantiating startpage that extends bootstrap, overwrite bootstrap? or is my syntax just wrong?

Controller (index page)

try {
    if (!include($paths['root'] . $paths['framework'] . '/core/AutoLoader.php')) {
        throw new Exception ('<b>Error - AutoLoader is missing</b>');
    }
    $loader   = new AutoLoader($paths);
    $appStack = new BootStrap($paths);
    $app      = new StartPage();
    $app->start();
} catch (Exception $e) {
    echo
        '<p><b>EXCEPTION</b><br />Message: '
        . $e->getMessage()
        . '<br />File: '
        . $e->getFile()
        . '<br />Line: '
        . $e->getLine()
        . '</p>';
}

Bootstrap class:

class BootStrap {
    protected $config;

    /**
     * --------------------------------------------------------------------------
     ** GETTERS
     * --------------------------------------------------------------------------
     *
     */
    public function getConfig() { return $this->config; }

    /**
     * --------------------------------------------------------------------------
     * __construct()
     * PUBLIC method
     * = Starts a new session, loads stylesheets, loads classes
     * --------------------------------------------------------------------------
     *
     */
    public function __construct($paths) {

        /**
         * --------------------------------------------------------------------------
         * load Config class
         * --------------------------------------------------------------------------
         *
         */
        try {
            if (!class_exists('Config')) {
                throw new Exception ('<b>Error - Configuration class is missing</b>');
            }
            $this->config      = new Config();
        } catch (Exception $e) {
            echo
                '<p><b>EXCEPTION</b><br />Message: '
                . $e->getMessage()
                . '<br />File: '
                . $e->getFile()
                . '<br />Line: '
                . $e->getLine()
                . '</p>';
        }
    }
}

Startpage class:

class StartPage extends BootStrap {

    /**
     * --------------------------------------------------------------------------
     * __construct()
     * PUBLIC method
     * = Starts a new session, loads stylesheets, loads classes
     * --------------------------------------------------------------------------
     *
     */
    public function __construct() {
    }

    /**
     * --------------------------------------------------------------------------
     * Start()
     * PUBLIC method
     * = loads the web page
     * --------------------------------------------------------------------------
     *
     */
    public function Start() {

        // path to includes
        $inc_path = $this->paths['root'] . $this->paths['medium'];

        // instantiate page, html header
        $charset     = $this->config->getCharset();
        $title       = $this->config->getTitle();
        $description = $this->config->getDescription();
    }
}

Answer 1

As soon as you give StartPage its own __construct() method, you effectively “hide” the one in Bootstrap, over-riding it completely. So $foo = new StartPage() only runs the __construct() code from the StartPage class.

In order to also run the __construct() code in the Bootstrap parent class, you have to add an explicit call to it, using parent::__construct().

In case you wonder why PHP doesn’t do this for you, here are three things you couldn’t do if it were automatic:

1. Run code both before and after the parent constructor, by choosing when to call parent::__construct().
2. Replace the entire constructor logic with something else while still inheriting the rest of the class.
3. Pass values into the parent constructor which are always the same / can be chosen automatically by the child class, but which would need to be provided explicitly to the parent class.

EDIT: To summarise the further clarifications below, creating a particular instance of the parent (Bootstrap) class will not make any difference to later creations of other instances of the same class or its child class (StartPage); each is a separate object and will call __construct independently.

If you want multiple StartPage objects to refer to one particular instance of the Bootstrap class, then inheritance is not the right mechanism. Instead, you will need to pass the created Bootstrap instance into each StartPage instance via some form of Dependency Injection.