Patterns are ways to describe best practices and good designs.
They show a flexible solution to common programming problems.
The Factory pattern allows for the instantiation of objects
at runtime. It is called a Factory Pattern since it is
responsible for "manufacturing" an object.
Example 19-23. Factory Method |
<?php
class Example
{
public static function factory($type)
{
if (include_once 'Drivers/' . $type . '.php') {
$classname = 'Driver_' . $type;
return new $classname;
} else {
throw new Exception ('Driver not found');
}
}
}
?>
|
Defining this method in a class allows drivers to be loaded on the
fly. If the Example class was a database
abstraction class, loading a MySQL and
SQLite driver could be done as follows:
|
<?php
$mysql = Example::factory('MySQL');
$sqlite = Example::factory('SQLite');
?>
|
|
The Singleton pattern applies to situations in which
there needs to be a single instance of a class.
The most common example of this is a database connection.
Implementing this pattern allows a programmer to make this
single instance easily accessible by many other objects.
Example 19-24. Singleton Function |
<?php
class Example
{
private static $instance;
private function __construct()
{
echo 'I am constructed';
}
public static function singleton()
{
if (!isset(self::$instance)) {
$c = __CLASS__;
self::$instance = new $c;
}
return self::$instance;
}
public function bark()
{
echo 'Woof!';
}
public function __clone()
{
trigger_error('Clone is not allowed.', E_USER_ERROR);
}
}
?>
|
This allows a single instance of the Example
class to be retrieved.
|
<?php
$test = new Example;
$test = Example::singleton();
$test->bark();
$test_clone = clone($test);
?>
|
|
Object Iteration
