单例模式是最常见的模式之一，在Web应用的开发中，常常用于允许在运行时为某个特定的类创建一个可访问的实例。
<?php
/**
* Singleton class
*/
final class Product
{
/**
* @var self
*/
private static $instance;
/**
* @var mixed
*/
public $mix;
/**
* Return self instance
*
* @return self
*/
public static function getInstance() {
if (!(self::$instance instanceof self)) {
self::$instance = new self();
}
return self::$instance;
}
private function __construct() {
}
private function __clone() {
}
}
$firstProduct = Product::getInstance();
$secondProduct = Product::getInstance();
$firstProduct->mix = ‘test‘;
$secondProduct->mix = ‘example‘;
print_r($firstProduct->mix);
// example
print_r($secondProduct->mix);
在很多情况下，需要为系统中的多个类创建单例的构造方式，这样，可以建立一个通用的抽象父工厂方法：
<?php
abstract class FactoryAbstract {
protected static $instances = array();
public static function getInstance() {
$className = static::getClassName();
if (!(self::$instances[$className] instanceof $className)) {
self::$instances[$className] = new $className();
}
return self::$instances[$className];
}
public static function removeInstance() {
$className = static::getClassName();
if (array_key_exists($className, self::$instances)) {
unset(self::$instances[$className]);
}
}
final protected static function getClassName() {
return get_called_class();
}
protected function __construct() { }
final protected function __clone() { }
}
abstract class Factory extends FactoryAbstract {
final public static function getInstance() {
return parent::getInstance();
}
final public static function removeInstance() {
parent::removeInstance();
}
}
// using:
class FirstProduct extends Factory {
public $a = [];
}
class SecondProduct extends FirstProduct {
}
FirstProduct::getInstance()->a[] = 1;
SecondProduct::getInstance()->a[] = 2;
FirstProduct::getInstance()->a[] = 3;
SecondProduct::getInstance()->a[] = 4;
print_r(FirstProduct::getInstance()->a);
// array(1, 3)
print_r(SecondProduct::getInstance()->a);
// array(2, 4)
原文：http://www.cnblogs.com/Czc963239044/p/7115696.html