Detailed explanation of singleton pattern in PHP

This article introduces the PHP singleton mode. The article explains the concept of the singleton mode, the characteristics of the singleton mode, the reasons and scenarios for using the singleton mode, and PHP singleton mode code examples. Coders in need can refer to the following

Detailed explanation of PHP singleton mode

The concept of singleton mode

The singleton mode refers to a certain class in the entire application that only Design pattern for an object instance. Specifically, as a method of object creation, the singleton pattern ensures that a 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 inside the singleton class.

Characteristics of the singleton model

The main characteristics of the singleton model are "Three private and one public":

Needs a private static member variable that holds the only instance of the class

Constructor functionmust be declared private to prevent an external program from newing an object and losing the meaning of a singleton

Clone functionMust be declared private to prevent the object from being cloned

Must provide a public static method to access this instance (usually named getInstance ), thereby returning a reference to a unique instance.

Reasons and scenarios for using the singleton mode

In most applications of PHP, there will be a large number of database operations. If the singleton mode is not used, then every time New operation is required, but each new will consume a lot of system resources and memory resources, and each time the database is opened and closed, it is a great test and waste of the database. Therefore, the singleton pattern is often used in database operation classes.

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

PHP singleton mode implementation

The following is a framework for PHP singleton mode to implement database operation classes

<?php
 class Db{
 const DB_HOST=&#39;localhost&#39;;
 const DB_NAME=&#39;&#39;;
 const DB_USER=&#39;&#39;;
 const DB_PWD=&#39;&#39;;
 private $_db;
 //保存实例的私有静态变量
 private static $_instance;
 //构造函数和克隆函数都声明为私有的
 private function __construct(){
 //$this->_db=mysql_connect();
 }
 private function __clone(){
 //实现
 }
 //访问实例的公共静态方法
 public static function getInstance(){
 if(!(self::$_instance instanceof self)){
 self::$_instance=new self();
 }
 //或者
 if(self::$_instance===null){
 self::$_instance=new Db();
 }
 return self::$_instance;
 }
 public function fetchAll(){
 //实现
 }
 public function fetchRow(){
 //实现
 }
 }
 //类外部获取实例的引用
 $db=Db::getInstance();
?>

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