Detailed PHP single-case mode

Singleton mode (Singleton pattern single-piece mode or single-element mode)

Singleton mode ensures that a class has only one instance, and instantiates itself and provides this instance to the entire system.

Singleton mode is a common design pattern, in the computer system, the thread pool, cache, log objects, dialog boxes, printers, database operations, graphics card drivers are often designed as a single case.

The singleton pattern is divided into 3 kinds: Lazy Type single case, a hungry man type single case, registration type single case.

So why use PHP singleton mode?

A major application of PHP is the application of the database to deal with the scene, there will be a large number of database operations in an application, the database handle connection to the database behavior, using a singleton mode can avoid a large number of new operations. Because each new operation consumes both system and memory resources.

Characteristics of the Singleton model

The main feature of the singleton mode is " three private One ":
Requires a private static member variable that holds a unique instance of the class
Constructors must be declared private to prevent external programs from being new to one object thereby losing the meaning of a singleton
The clone function must be declared private to prevent the object from being cloned
You must provide a public static method that accesses this instance (typically named getinstance), which returns a reference to the unique instance.

Reasons and scenarios for using singleton mode

In most of the PHP application there will be a large number of database operations, if not a singleton mode, that every time to new operations, but each time new will consume a lot of system resources and memory resources, and each open and close the database is a great test and waste of the database. Therefore, singleton patterns are often used in database operation classes.
Similarly, if a class is needed in the system to control some configuration information globally, it can be easily implemented using singleton mode.

PHP Single-instance mode implementation

The following is a PHP singleton schema implementation of database operation class framework

<?php class db{const db_host= ' localhost '; const db_name= '; const db_user= '; const db_pwd= "; private $_db;//Save Instance Private Static variable private static $_instance; Constructors and clone functions are declared private function construct () {  //$this->_db=mysql_connect ();} Private Function Clone () {  //implementation}//access to the public static method of the instance getinstance () {  if (! Self::$_instance instanceof Self) {  self::$_instance=new self ();  }  or  if (self::$_instance===null) {  self::$_instance=new Db ();  }  return self::$_instance; } public Function Fetchall () {  //implementation} Public function Fetchrow () {  //implementation}}//class external Get instance Reference $db =db::getinstance (); >