PHP: How to prevent multiple instances of extended class - php

Question

I have a class that contains methods used globally, and am using them by extending the class:
App.php
final class App extends Core {
// The app class handles routing and basically runs the show
}
Core.php
abstract class Core {
public function __construct() { // Here we bring in other classes we use throughout the app
$this->Db = new Db($this);
$this->Mail = new Mail($this);
}
// Then we define multiple methods used throughout the app
public function settings($type) {
// You see this used by the model below
}
}
index.php
$App = new App(); // This fires up the app and allows us to use everything in Core.php
Up until now, this is all great, because everything is handled throughout the site from within $App. However, within my MVC structure, the models need to pull data from the database, as well as retrieve other settings all contained in Core. We do not need the entire $App class to be used by the models, but we need Core to be.
MyModel.php
class MyModel extends Core {
public function welcome() {
return 'Welcome to '.$this->settings('site_name');
}
}
Once MyModel.php comes into play, the Core constructor is run a second time. How do I keep the Core constructor from being run twice?

Answer 1

you can use a static instance in the core class and reuse it.
abstract class Core {
public static $instance; //create a static instance
public function __construct() { // Here we bring in other classes we use throughout the app
$this->Db = new Db($this);
$this->Mail = new Mail($this);
self::$instance = $this; // initialise the instance on load
}
// Then we define multiple methods used throughout the app
public function settings($type) {
// You see this used by the model below
}
}
in the model class, use it like this
class MyModel extends Core {
public function welcome() {
$_core = Core::instance; // get the present working instance
return 'Welcome to '.$_core->settings('site_name');
}
}
you can take a look at this singleton reference
additionally you can check this answer explain-ci-get-instance