singleton.php

<?php
class Single
{
  private static $instance;

  private function __construct()
  {
    self::tetete();
  }

  public static function getInstance()
  {
    if(!isset(self::$instance))
    {
      self::$instance = new Single;
    }
    return self::$instance;
  }
  public function tetete()
  {
    echo 'tetete';
  }
}
$a = Single::getInstance();
$b = Single::getInstance();
if ( $a === $b )
{
  echo 'true';
}