PHP Patterns (Factory & Singleton)

Factory

定义：

<?php
class 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

定义：

<?php
class 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);

?>