Getting Started with PHP Design Patterns - Singleton Pattern_PHP Tutorial

Introduction to PHP design patterns - singleton pattern

In the daily development process, we often encounter some classes that do not need to be instantiated repeatedly, such as database connections. In this case, the singleton mode is the best solution. I happened to be asked about this model in my last interview, so I will summarize it here today.

Let’s first look at the implementation of the simplest singleton pattern:

<!--?php
class Singleton{
     static $instance;

     static function getInstance(){
          if(is_null(self::$instance)){
               self::$instance = new self();
          }
          return self::$instance;
     }

}

$test1 = Singleton::getInstance();
$test2 = Singleton::getInstance();

if($test1 === $test2){
     echo 是同一个对象;
}else{
     echo 不是同一个对象;
}
</pre-->

运行结果如下：

But just writing it like this is not a true singleton pattern in a strict sense, because users can instantiate new objects through the new keyword.

$test1 = new Singleton();
$test2 = new Singleton();

The running results are as follows:

So we have to make a little improvement to our code and set the access level of the constructor to protected:

<!--?php
class Singleton{
     static $instance;

     protected function __construct(){
         
     }

     static function getInstance(){
          if(is_null(self::$instance)){
               self::$instance = new self();
          }
          return self::$instance;
     }

}

$test1 = new Singleton();
$test2 = new Singleton();

if($test1 === $test2){
     echo 是同一个对象;
}else{
     echo 不是同一个对象;
}
</pre-->这时当用户试图以new关键词实例化一个新的对象时，会报如下截图所示的错误：

Of course, cunning users can still clone a new object through the clone keyword:

$test1 = Singleton::getInstance();
$test2 = clone $test1;

if($test1 === $test2){
     echo 是同一个对象;
}else{
     echo 不是同一个对象;
}

Running results:

So we also need to declare the __clone method as protected:

<!--?php
class Singleton{
     static $instance;

     protected function __construct(){
         
     }

     static function getInstance(){
          if(is_null(self::$instance)){
               self::$instance = new self();
          }
          return self::$instance;
     }

     protected function __clone(){
         
     }

}

$test1 = Singleton::getInstance();
$test2 = clone $test1;

if($test1 === $test2){
     echo 是同一个对象;
}else{
     echo 不是同一个对象;
}
</pre-->时当用户试图以clone关键词克隆一个新的对象时，会报如下截图所示的错误：

So to implement a singleton pattern in a strict sense, you should pay attention to the following points:

1. Declare the constructor as protected;

2. Create a static method of getInstance to obtain the static variables that save the class;

3. Declare the __clone method as protected

Of course, in actual development, in most cases it is enough to implement a simple singleton pattern (the way the first example is written).

http://www.bkjia.com/PHPjc/1040917.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/1040917.htmlTechArticleIntroduction to PHP Design Pattern - Singleton Mode In the daily development process, we often encounter some classes that do not need to be repeated. Instantiated, such as a database connection, in this case, the singleton pattern is...