Example custom singleton on php

SampleSingleton.php

class SampleSingleton
{
    private static $_instance = null;
 
    private function __construct()
    {
    }
 
    public function getInstance()
    {
        if (!(self::$_instance instanceof SampleSingleton)) {
            self::$_instance = new SampleSingleton();
        }
 
        return self::$_instance;
    }
}