Getting Started with PHP design mode-Singleton mode

In the daily development process, often encounter some classes do not need to re-instantiate, such as database connection, in this case, the singleton mode is the best solution. Just the last interview has been asked about this model, today to make a summary.

Let's take a look at one of the simplest implementations of the singleton pattern:

   
The results of the operation are as follows:
  

  
But this is strictly not a true singleton pattern, because the user can simply instantiate new objects by using the newly keyword.
  
  
$test 1 = new Singleton (), $test 2 = new Singleton ();
The results of the operation are as follows:
  
  
So we're going to make a little improvement on our code to set the access level of the construction method to protected:
  
  
  When the user attempts to instantiate a new object with the newly keyword, the error is reported as follows:
  

  
Of course, a cunning user can still clone a new object by using the Clone keyword:
  
  
$test 1 = singleton::getinstance (), $test 2 = Clone $test 1;if ($test 1 = = = $test 2) {     echo "is the same object";} else{     echo "Not the same object";}
  
Operation Result:
  

  
So we're going to declare the __clone method as protected:
  
  
!--? phpclass singleton{static $instance;                protected function __construct () {} static function getinstance () {if (Is_null (self:: $instance)) {          Self:: $instance = new self ();     } return Self:: $instance; } protected function __clone () {}} $test 1 = singleton::getinstance (), $test 2 = Clone $test 1;if ($test 1 = = = $ TEST2) {echo "is the same object";} else{echo "Not the same object";}  When a user attempts to clone a new object with the Clone keyword, the error is reported as follows: 
 
 
 
 
 
 Therefore, in order to implement a singleton pattern in strict sense, we should pay attention to the following points: 
 
 1, declare the constructor as protected; 
 
 2, create a static method of getinstance to get the static variable that holds the class, 
 
 3, declare the __clone method as protected 
 
 Of course in actual development, In most cases, you can simply implement a simple singleton pattern (the first example is written). 
 
 
 
 Copyright notice: This article for Bo Master original article, without Bo Master permission not reproduced. 
 
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