PHP design pattern singleton mode (single element mode)_PHP tutorial

php design pattern singleton mode (single element mode)

Single case mode:

As an object creation mode, the singleton mode ensures that a certain class has only one instance, instantiates itself and provides this instance globally to the entire system. It does not create a copy of the instance, but returns a reference to the instance stored internally in the singleton class.

(1). A static member variable that holds the only instance of the class is required: private static $_instance;

(2). Constructors and clone functions must be declared private to prevent external programs from creating new classes and thereby losing the meaning of the singleton mode:

private function __construct()

{

$this->_db = pg_connect('xxxx');

}

private function __clone()

{

}

(3). A public static method (usually the getInstance method) must be provided to access this instance, thereby returning a reference to the unique instance:

public static function getInstance()

{

if(! (self::$_instance instanceof self) )

{

self::$_instance = new self();

}

return self::$_instance;



}

Why use PHP singleton pattern?

1. PHP is mainly used in database applications, so there will be a large number of database operations in an application. Using the singleton mode can avoid a large number of resources consumed by new operations.

2. If a class is needed to globally control certain configuration information in the system, it can be easily implemented using the singleton mode.