PHP Patterns (Factory & Singleton)

Factory

定義：

<?phpclass Example{    // The factory method    public static function factory($type)    {        if (include_once 'Drivers/' . $type . '.php') {            $classname = 'Driver_' . $type;            return new $classname;        } else {            throw new Exception ('Driver not found');        }    }}?> 

使用：

<?php// Load a MySQL Driver$mysql = Example::factory('MySQL');// Load a SQLite Driver$sqlite = Example::factory('SQLite');?> 

 

 

Singleton

定義：

<?phpclass Example{    // Hold an instance of the class    private static $instance;        // A private constructor; prevents direct creation of object    private function __construct()     {        echo 'I am constructed';    }    // The singleton method    public static function singleton()     {        if (!isset(self::$instance)) {            $c = __CLASS__;            self::$instance = new $c;        }        return self::$instance;    }        // Example method    public function bark()    {        echo 'Woof!';    }    // Prevent users to clone the instance    public function __clone()    {        trigger_error('Clone is not allowed.', E_USER_ERROR);    }}?> 

使用：

<?php// This would fail because the constructor is private$test = new Example;// This will always retrieve a single instance of the class$test = Example::singleton();$test->bark();// This will issue an E_USER_ERROR.$test_clone = clone($test);?>