Question

This is the singleton pattern also named as the singleton class. Its goal is to allow only one object of type singleton. If there is already one and I call it, I’d like it to error out in some way. This won’t happen in production but in development. Is there a better way then just saying echo echo “Error:only one connection”;

class singleton
  {
  protected static $_db_pointer = NULL;
  private function __construct()
    {
    $this->_db_pointer = mysql_connect(DB_HOST, DB_USER, DB_PASS);
    mysql_select_db(DB_DATABASE);
    }
  public static function get_instance()
    {
    if(self::$_db_pointer == NULL)
      {
      return new self();
      } 
    else
      {
      echo "Error:only one connection";
      }
    }
  }

Answer 1

Exceptions usually are better.

else
{
  throw new Exception("Error:only one connection");
}

You can also use “LogicException”, “RuntimeException”, and a few others.

Further reading:
http://www.php.net/manual/en/language.exceptions.php

Another approach with singleton class is just to return the object instead of creating a new instance if one exists.