Singleton pattern in php

1. The origin of the singleton pattern

Class is an abstraction of a class of things with common characteristics in real life. Through the instantiation of a class, many objects are generated, but at the same time it also consumes a lot of resources (such as the limit on the number of connections when connecting to the database , and for example, opening the resource manager on the computer has uniqueness), which also resulted in the need to limit the instantiation of the class. In order to protect the uniqueness of resources, single case mode was born.

2. Definition of singleton pattern

Definition: Singleton pattern is a design idea that a class design will only produce at most one object.

3. Instance of singleton mode

a. Create an empty class.                                                                            

b. Being able to instantiate a class multiple times is the reason why multiple objects are generated, so you can privatize the

constructor method.

<?php
   class Use{
   }
   $a=new Use();//实例化一个对象
?>

c. Privatization

Constructor methodmakes the number of instantiated objects generated to 0, so that the constructor method can be called through static method inside the class , and then return the constructor to the outside.

<?php
  class Use{
    private function __construct()
    {
      echo __FUNCTION__."<br>";
    }
   }
?>

d. Although the object can be instantiated through the above method, it also releases the use rights of the constructor method. If you want this method to return only one object, you must ensure that there is a way to store a generated object inside the class. A new one is generated for the first time, and the old one is returned later. In this case, you need to use static properties.

<?php
  class Use{
    private function __construct()
    {
     echo __FUNCTION__."<br>";
    }
    public static function getInstance()
    {
      return new self();
        }
   }
  $s1=Use::getSingleton();
?>

e. At this time, it can be guaranteed that only one

object will be obtained by calling the static method. However, you can still instantiate new objects through clone, so you can privatize clone.

<?php
  class Use{
    private static $object = NULL;//初始化为NULL，没有对象 
    
    private function __construct()
    {
      echo __FUNCTION__."<br>";
    }
    
    public static function getInstance()
    {  
      //判断类内部的静态属性是否存在对象
       if(!(self::$object instanceof self)){   //当前保存的内容不是当前类的对象
       self::$object = new self();
    }
      //返回对象给外部
       return self::$object;
    }
   }
  $s1=Use::getSingleton();
?>

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