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:

<?phpclass singleton{     static $instance;     static function getinstance () {          if (Is_null (self:: $instance)) {self               :: $instance = new self ();          }          Return self:: $instance;     }} $test 1 = singleton::getinstance (), $test 2 = singleton::getinstance (), if ($test 1 = = = $test 2) {     echo "is the same object";} else{     echo "Not the same object";}

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:

<?phpclass singleton{     static $instance;     protected function __construct () {              }     static function getinstance () {          if (Is_null (self:: $instance)) {               Self:: $instance = new self ();          }          Return self:: $instance;     }} $test 1 = new Singleton (), $test 2 = new Singleton (), if ($test 1 = = = $test 2) {     echo "is the same object";} else{     echo "Not the same object";}

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 = = = $test 2) {     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 achieve a strict implementation of a single-case model, we should pay attention to the following points:

1, declare the constructor function 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 the actual development, in most cases as long as the implementation of a simple singleton mode (the first example of the wording).

Copyright NOTICE: This article for Bo Master original article, without Bo Master permission not reproduced.

Getting Started with PHP design mode-Singleton mode