A simple way to store variables in a class

config.php

abstract class config{
    protected $myconf = array();
    abstract function getValue($key, $default="");
    abstract function setValue($key, $value);
    abstract function clearConfig();
}

myClass.php

require_once 'config.php'
class myClass extends config{
    public function getValue($key, $default = "") {
        if(isset($this->myconf[$key]) && !empty($this->myconf[$key])){
            return $this->myconf[$key];
        }else{
            return $default;
        }
    }

    public function setValue($key, $value) {
        $this->myconf[$key] = $value;
    }
    
    /**
     * Clear the stored data
     */
    public function clearConfig() {
        $this->myconf = NULL;
    }
    /*
    More methods
    */
}